Jaske!
J and I are in a debate on what it is but my vote is canker sores, can be from nerves, or an allergy or both. J says it's bacteria from the toothbrush but I said if that is so then why aren't the antibiiotics working to kill the bacteria? SO...I suggest rinsing and gargling with salt water.
Nice to see you kiddo! Take care and let us know how this resolves, but again, I think it sounds exactly like canker sores and your nerves made them get worse. Try the salt water, warm salt water rinse that is.
Good luck!