I recently had an ultrasound right breast & axilla. a few days later large painful red bumps(like extremely large pimples) developed. i used baking soda paste to bring them to a head. i didn't pop them bc too painful?

Problem occurred after you had had the US done so either you are allergic to the gel (rarely seen) or you have a superficial skin infection. Contact dermatitis (allergy) causes rash and itching not painful pimples and soda paste probably made thing worse. You should see your doctor for a proper care.

GENTLY wash theses with a soft cotton washcloth and antibacterial soap, such as Dial Antibacterial or Lever 2000. Let the shower hit these “pimples” (not too hard as to hurt) and they should be gone in a few days. Best to you!