My finger is sore and swollen at the knuckle (right - index) and it have been for over a week. there's pain when i bend it (as if i'm trying to pop my knuckles) but i can bend it no other finger on this hand or the opposite is like this. a strain?

If you are in the habit of popping your fingers you should stop because you may have inadvertently caused injury that may be the reason you have pain. The fact that it is one finger suggests injury, however there is possibility of infection but you did not include any symptom to suggest infection. Time and care should allow healing.

This sounds like a bruise or strain, however, if there is redness or you have a fever, it could be infected. Also, as we don't know your medical history or if you have had other joints affected now or in the past, if this continues, or if that is the case (other affected joints), you should have this examined and discuss with your doctor to be sure it is not more than those possibilities.