Can you help me?

Two years ago, my teenaged son had a couple of fingers and a toe that were swollen. At one point one finger was so swollen, he couldn't straighten his hand. It was like the tendons were tight. The doctor put him on steriods and took blood and xrays. Everything came back fine,no arthritis. I was so thankful but still didn't know the cause. Eventually all went back to normal. Then last year in February, the same thing. It wasn't as bad but a few fingers were swollen again. This morning his pinky finger is swollen and he told me a toe was last week. Does anyone have any idea what this could be? I've googled and googled and can't find an answer. If you have any ideas please let me know. I've worried about this for 2 years and I'm not sure of what to do next. Thanks~Fran