It has been 3 years now i constantly get my right innermost lateral tongue irritated, it heals and again gets irritated and red.

A few thoughts: If you have gained a lot of weight, it is possible that your tongue has enlarged w/ the rest of you & is now rubbing on your teeth in a different way than it was before. If you've had a change in your bite for some reason, you may need to have it checked out by a dentist. Worst case would be possible inflammation like from tobacco that would need to be seen by an ent. Maybe your fp can sort it out.

Bite?: My best guess is trauma from your bite. Next best is allergy, finally something to biopsy. Check with your doctor for a diagnosis.