I kinda get what your going through because it seems that I would often get nightmares as well. But it is certainly not the only dreams you have had. Whether you choose to believe this or not. This might sound strange, but when you sleep you always dream about something no matter what, even though it may seem some days you didn't have one. You can have 2, 3 or even more dreams in one night. Like me you just happen to remember only the nightmare aspect than the good. Which makes it seem like your only getting nightmares all the time. Its because your nightmares leave off a really bad impact, certainty something frighting to remember, where in some cases you wake up gasping.

So it may seem your only getting nightmares because you plainly don't remember the other 2 or more dreams you have had in that one night. It's like you have no memory of it, completely wiped from the head. But regardless I hear you, nightmares are no fun as you can clearly see, they leave to much of an impact pushing out all the good. Hopefully it will some come to pass for you.