Acne - Scab - Welt.......................?

Hi! I have acne ( had it for like 2 years ) and now, im getting alot of them on my back and chest area. However, im also getting these hard welts that dont hurt. (most of them were scabs first, but someone became a welt o.O? like i kept washing it off and it broke alot..) So any idea what the welts are?? Thanks