Last night was lying in bed bf ds who is nearly 18 mo and bf at night only. Found a small lump between boob and armpit, quite hard, size of a ball bearing. Was about 3am and I was hot and tired and couldn't get back to sleep. Worried for a while. It was quite tender but I had been pressing and feeling it for a while. Finally got back to sleep and this morning I can't find it. The whole area is tender if pressed but not lump. Should I go to doc? Do they take seriously if you can't find it any more? Or can such things disappear?