Ok see your GP,
and when you lift anything try and do it with your forearms uppermost. Basically tennis elbow is (now remember I was an Army paramedic so im not an expert hence my insistance on you seeking profesional advice) is where the muscle stats to detatch from the tendon holding it to the bone (humeros/elbow). In my case it detatched 100%, it almost made me cry, it took weeks of physio and in the end a steroid injection to put it right. I've lost about 15% of the power I had before that, yours sounds like a mild form but you need to see a GP as it will not get better without medical help (as I found out to my detrement).
As I said, let me know how you get on
Xx