Wow almost identical situation -- a lump in my breast that looks like an insect bite appeared overnight  6 weeks ago. It got bigger and then a second identical lump turned up on my other breast. Got through to the GP and had an exam, they told me it was probably a localised infection caused by big breasts and friction.  Unfortunately the swelling had gone down slightly and the GP said they could not feel the lumps even though I had picture evidence. 
 

Two weeks later, lumps are back and the area is tender and swollen. I'm sure it's just hormonal, as are yours, but would also really like to get some proper clarification. I'm going to call my GP back tomorrow - I'd recommend doing the same and stressing that the area feels tender etc. Because they're so quick to dismiss younger women! Hopefully just a cyst etc. but I've also had some awful anxiety around it.