You really need to see a dentist. If there is an abscess, you will need antibiotics.
PLEASE don't let this go. I did, in a front tooth, and not only did I loose that one, but three others because the infection spread to the bone.
It may be something as simple as needing your teeth cleaned and some antibiotics to clean up the infection but if you wait you run the risk of it infecting more teeth and much bigger problems later.
No one should be in pain.
Please call your dentist.