I have a lump on my forearm muscle and im kind of worried about it. Only hurts when I press it. Arm feels perfectly fine other than that lump. Clues?

See a specialist. See a hand/upper extremity or orthopaedic surgeon. While most lumps and bumps turn out to be benign, some are serious. If there is any question, get the opinion of an orthopaedic oncologist, a person who cares for tumors of bones, joints, muscles. Proper care of the serious lumps care increase the chance of good outcome.