Is it normal to develop lumps when breastfeeding?

Nursing. Yes, they are usually milk cysts which are cystic diatations of the milk ducts that are not draining completely with feeding. You can use warm packs and massage towards the nipple to get the milk out. Not ot alarm you, but if it doesn't resolve in a couple of days with above, tell your doctor, you may need an ultrasound to be sure it's not solid.
Yes. It happens quite a bit- but it is easy to have them checked by a breast surgeon to make certain they feel normal.