What might be the cause of a recurring soreness on the left side of the tip of my tongue? apples, red wine, nuts, etc. worsen the problem.

See dentist: Could be canker sore, small ulceration that is tender, heals in 7-10 days; trauma from teeth; superficial or deeper abnormality; much less likely referred pain, etc. Smoker? Hpv? White lesion? Seedentist first. If need biopsy, oral surgeon.

Many causes.: Many possibilities. Some are too much acid, rough spot on a tooth or removable denture, diabetes... The list goes on. This is a problem that needs a dentist to examine you to determine the cause and the proper method of fixing. Make an appointment!