Abscess on Gums? Is this an emergency?

I had wisdom tooth surgery back in July, and since then every once in a while I get these little white "lumps" right above the surgical site. They seem to be pus-filled, and they usually drain on their own (I asked my dentist about it after one drained before, and he prescribed an antibiotic for it).

Anyways, the last few days, I noticed the "lump" has returned; only this time it actually hurts a bit, and it doesn't seem like it wants to drain. Is this another abscess? If it is, do I need to go back to my dentist? Also, if it is an abscess, does that constitute a dental emergency?

Thanks!