pimple like bumps under armpts??

Did you shave at all under your arms recently?  If so, you may have razor burn from the shaving. You will want to use shaving gel or lots of soapy bubbles when you shave next time.  Use hydrocortisone cream for the inflammation and itching.  If you didn't shave, you may have some ingrown hairs that have become infected.  You will need to exfoliate the area to loosen the hairs then keep the area clean until the "pimples" heal up. You will want to use some antiseptic if you decide to lancet the areas to rid of the infection.  I hope this helps!