It is the rider not the bike... except when we're talking about Walmart bikes. OP probably has a heavy hunk of poorly assembled junk.

guinallen, check out the selection at real bike shops, or at least real sporting good shops like REI. You don't need to think about a specific brand. Your budget is below what I would call realistic, but not by much. You can get something fun and serviceable for $600 or so. And you don't need disk brakes or a suspension fork. And don't get it on-line because you don't know what you don't know and you'll likely be disappointed again.