I hv a yellowish lump on the wall of my mouth just beside my last premolar teeth. it is very painful and i can't chew properly. what is this, ?

See your dentist: We can't diagnose your problem without actually seeing you. You will have to visit your dentist to find out what it is. Even if we knew what it was, you will probably require treatment by a dentist. It could be many things, and especially if it's an infection, don't delay making that call to your dentist.

Possible abcess: Dr sanders is right. It is difficult to diagnose the problem without seeing the lesion or lump, it location(wall?), and various signs that may help to determine the source. A swelling of the gums on the side of tooth with tenderness to chewing or pressure often time indicates a abcess or infection in tooth socket. Yet there are other possibilities. See the dentist for treatment.

This is one of those situations where an in-depth examination, thorough review off your medications as well as an all inclusive Medical/Dentil History is required. You may also require imaging as well as lab tests. There are numerous possibilities, some benign, some not. Be prepared to answer how long you have had the lesion, and has it changed in size/color/shape/texture recently. See Dentist now