header glitch

Hello!
Ive been trying to replace my default wordpress header and have tried it with different plugins, but each time i do it causes my site to glitch. For some reason it mainly effects my peepso activity stream (the parts where my wordpress posts are shared), the header will appear in multiple areas throughout that page. It also causes all pages of the website (not just peepso) to slide too much to the right instead of the position being fixed. Im wondering if anyone has had a similar issue or can give advice on how to fix it. much appreciated.