Many times, the first symptom of bacterial pneumonia IS back pain (see comment below by George Sooley to explain why you feel that pain). Viral pneumonia is not as well known for causing back pain, you actually may not have any at all! Our bodies interpret lung irritation as back pain, which may get worse as the inflammation spreads. You may even go to the doc, thinking you have a back strain, and please note, some people in the early stages of pneumonia are misdiagnosed with a back strain at first! Be sure to share anything you have noticed, fever, being exposed to others with known pneumonia, the beginnings of a cough, etc.
Bacterial pneumonia also causes fluid in the lungs, which generally makes it harder to breathe, and this certainly does not help with back pain, as you use muscles that you do not normally use to breathe (called accessory muscles), due to decreased healthy lung space that can exchange carbon dioxide for oxygen, so you may feel short of breath. Get to the hospital right away for SOB (Shortness Of Breath) that does not go away on its own (when not exerting). If the SOB never leaves, get to the hospital! One way to check if a person is getting enough oxygen, is to take their WARM (not cold) hand (rub their hand between yours until nice and warm, if needed, until the hand is warm to touch, so you can check capillary refill. Capillary refill is seeing how fast the small blood vessels refill after brief pressure is applied to specific areas of the body, usually the fingers or toes, on the nail. The hand or food MUST be warm to touch, as blood does not flow well to fingertips or toes when the area is cold, and will give you incorrect information. Try this on yourself first so you know what you are looking for. Pinch down on the end of the digit with decent pressure, not to cause pain, but to squeeze the blood out of the capillaries (tiny blood vessels), over the nail for about a second or two, and release. The white color now under the nail (blanching) should return to the same pinkish color as under the other nails in under 3 seconds, and if not- if it takes longer in a warm appendage (and this is abnormal for them- something a doctor has not told them is normal due to diabetes or cardiovascular issues), then a hospital visit is probably needed if the SOB is still a problem, and they are visibly having issues, or especialy if they are getting tired due to problems breathing. Call an ambulance if you think it is necessary if it gets serious to this point. Bacterial pneumonia is extremely contagious, so if diagnosed and sent home, everyone visiting should use a mask to breathe (surgical masks are cheap, and can be bought at almost any drugstore), until the doctor says the patient is no longer contagious. Anyone with COPD, severe asthma, on oxygen, on chemo, or with other lung issues should be asked not to visit, as it can be life threatening for some people, but only while contagious.
If the sick person known to have a contagious infection such as this goes out in public, they can easily make others very sick. Please stay home unless a hospital visit is needed. Others with compromised immune systems can get very, very sick from catching this illness if they have a serious chronic illness, and you cannot tell by looking at a person if they have a chronic illness. Do not force the ill person with pneumonia to wear a surgical mask if unwilling due to SOB in public, but at least try to keep them away from others in the waiting room and make sure they practice good hand hygiene (cough into thier sleeve, not hands or , worse, an uncovered mouth while coughing or sneezing, etc).
Coughing repeatedly and sneezing can also cause back pain on top of the irritation this illness already causes, it can cause strained/pulled muscles or muscle spasms in the chest and back (sometimes severe). Did you know it is possible to cough so hard that you can actually crack a rib?!?! It is true! If, after your contagious period has passed, and you have a nagging pain while breathing that will not go away, especially if it interferes with your taking full breaths, you will probably want to go to the doc (if not, call the nurse to see if your doc wants to see you, please do one or the other!!), just in case, to check for secondary problems. Now, for a cracked rib, there is not much they can do treatment wise, but at least you know what is wrong , and you know you have to take it easy. It is important that you be able to take full breaths when recovering from pneumonia, so let your doc know if this is not happening for any reason, If you are not yet able to take full breaths due to pain, and you should be able to by this time, according to the doctor, this needs not be ignored. This is VERY important! Whether it is illness or a cracked rib, you may have to practice breathing normally, and he/she may give you a device to practice breathing deeply several times a day to help fill your lungs fully. This instrument is usually given when hospitalized, but I have seen it given and used at home as well. Follow your doctor’s instructions.