Getting small liquid bubbles in mouth along with huge ulcer that hasn't healed. the roof of my mouth, in the middle, also hurts. is this serious?

Diagnosis?: These types of situations require a personal one on one medical history and clinical exam. Since we can't do that over the internet you need to see an oral surgeon (or ENT specialist).

Get diagnosed first: While what's described sounds much like hsv (herpes simplex virus) infection, without having done correct data gathering and exam, no diagnosis can be given, unfortunately. Whether your condition is serious or not cannot be determined without diagnosis. Ulcers that do not heal need to be examined. This may be very contagious to other areas and other people as well, so please see a doctor asap!