Whenever i eat my mouth clenches up stiff & it takes quite an effort before i can open my mouth again so i can chew. it gets painful as i continue eating & having my jaw lock up my mouth closed with every bite. why is this happening? any treatments?

It is not feasible to provide a meaningful opinion without additional history, physical examination and may be some tests. It would be prudent to see a dentist. Wish you good health!

Among possibilities are joint disk displacement, near-muscular malfunction, pernicious habits, Malrelationship of teeth and/or jaws, arthritis, etc. See your Dentist for initial evaluation. Imaging may be advantageous. Specialist(s) referral may be indicated.