I keep feeling my heartbeat (or pounding) in the top or back of my head. what could cause this? no headache though

Head congestion: Most likely you have a blocked eustachian tube ( the connection between your middle ear and throat that "pops" when you go up a mountain.) if you're getting over a cold, that would explain it. If not, and it persists, you should be checked for a more serious but rare cause (like an aneurysm) but it's very unlikely that you have that.