What can i do to relieve severe tendonitis in my forearm?

Tendinitis: Consider anti inflammatory drugs like advil (ibuprofen) or alleve, heat, physical therapy and sometimes cortisone injection. See your doctor.

Time/rest/NSAIDS: Usually tendinitis will improve over time with rest, activity modification, and use of Ibuprofen type meds. If this does not work and depending on the location of the tendinitis, injections of cortisone are sometimes used. If this fails, a few types of tendinitis can be treated surgically, but this is rare in the forearm and usually not necessary. See your doctor if it doesn't improve.

While I agree..: While i agree with dr. Slattery, you can not ignore the fact the extensor muscles and tendons have been overloaded. It is important to do forearm strengthening, best done with a polyurethane or rubber hand grip: 20 grips, 2-3 times per day.