I have pain in my elbow and my forearm from ulna side when i bent my arm for like 30 min i feel pain i have to sleep with arms straigh what itcould be?

Olecranon bursitis: This may be a bursitis (inflammation of a fluid filled "cushion " in the ulnar radial (elbow) joint! See an orthopedist!!!!!! A simple injection can help!!

Tendon/muscle strain: Sometimes when you are forced to keep your arm or leg in a set position, without moving for a prolonged period you can strain the tendons/ligaments. Perhaps your elbow was even "over" flexed...bent too far. We would normally expect this to resolve fairly quickly within a day or two. It sounds like you are now having trouble bending/flexing your elbow joint. You should seek evaluation from your doc