Unexplained bruising on thigh

My husband has had  long term problems going on and I am starting think perhaps they are all related. First off, 3 months ago he started feeling severely depressed with suicidal thoughts. He is a manager of a huge retail chain so he is under tremendous stress constantly and I believe suffers from mild anxiety now. 2 weeks ago he started to have pain in his left arm that radiated to his chest for a few days before moving into the upper middle part of his back. We went to the doctor last Tuesday and she diagnosed him as bipolar and prescribed him lithium 300mg 2x per day. She had mentioned checking his blood for thyroid problems and anemia but never did. Right when he got home Wednesday, he hadn't take the first dose of Lithium yet, he had a small bruise on his right thigh. As the day went on the bruise started to swell and it became like a knot but it grew and another one appeared right next to it, both about the size of my fist. Today this bruise is still there but is more purple and green but the center still has red bruising. He doesn't remember ever hitting it or having any trauma to that area, no sign of insect bite, and doesn't appear to be a blood clot. Does anyone know what this is? Any idea if its related to the recent health issues? Im extremely worried about him and he doesn't want to go back to the doctor.