3 month old throwing fits?

I was seriously just thinking this. My son is going to be 11 weeks on Friday and just starting like three days ago he has been doing the same thing. I know that nothing is wrong with him. He will kick his legs down against my stomach and stand up so I have to move his legs out so I can actually burp him. I will be watching your answers. Sorry that I don't have an answer for you since I am going through the same thing! :-)