My mum gets mouth ulcers really badly - and the doctor has given her something to take for it - and am sure there is something she is deficient in (will ask her when UK wake up) - so yes I would go back.

The other thing is - any chance you have never been exposed to Hand, Foot, Mouth virus before and have recently - e.g. via the kids (is rife round daycare normally)? My DD that was the only symptom a mouth full of ulcers - doc said a chance you can get as adult but not that likely because most people have early on in life.