I have forearm pain in my rightarm?

Over the last 6-9 months my right forearm has been getting more and more painfull, It's now got to the point that I can't lift a cup without imense pain sweeping through it. It's painfull to grab, lift extend my arm. I have been using an anti-inflamatry gel (Diclofenac diethylammonium) but this isn't helping. Can anyone tell me what might be wrong?