Want to try different positions!

Here's the deal. When me and my boyf have sex, I'm always on top. Always. I think only about 3 or 4 times has he been on top. It's kind of getting to me a little, because I at least want him on top or I want to try something like doggy style. However when we tried him being on top the other day, it didn't work, it seemed like he couldn't stay hard or something, so I went on top and it worked fine. So I have two questions. 1) does playing sport the day before affect how a guy can have sex? (That's generally the reason he gives.) 2) are there any positions that don't mean I'm on top? I don't feel like I'm very good at it, and I want to try something new. Thanks for your help.