I had a lump under my armpit but its going away.?!

Using antiperspirant (not deodorant) can plug up the sweat glands and cause inflammation. Just make sure you wash your armpit with warm water and soap.

In the same area, you have lymph node. This, in case of infection, helps absorb the unhealthy secretions (inside your system). Just the fact that the area got better fast does not mean that the cause is gone, just the symptom.

For my part, I used to have bumps like that under my right armpit. I got so anxious about it, I now shave my armpit. That way i can really get rid of all the protection I put under there.

It would not hurt to have a M.D. check it should you have another flare-up or you felt pain in the area again.

Good luck.

probably just an ingrowing hair or boil or large spot, if it's going away, that has to be a good sign. if you're really worried though, go to the doctor.

probably just caked-on deodorant

have a shower dude