I know exactly what you're going through, Caty. I felt all of the same depressing thoughts as you; that God would forsake me for thinking these thoughts and that I would go to hell for the unwanted thoughts, that I was totally unforgivable and not worthy of being forgiven. I even resorted to physical pain to distract from these thoughts.
You have to realize that these thoughts aren't of your own. You don't want these thoughts and they're not of your heart. Religious OCD is a disorder, and you can overcome it. You have to blame this on your OCD. Don't put this horrible blame on yourself. Once you do that, it becomes so much better and easier to deal with.
Whenever you have one of these bad thoughts, you have to tell yourself, "This is just my OCD." Or something along those lines. When you do this, you take away the importance you've been putting on these thoughts. Just brushing them off as though they're nothing, telling yourself that they're nothing, will eventually make it so in your mind. I hardly ever have OCD thoughts anymore concerning my religion, and you can get to this point as well.
Like everyone else in this thread said, God loves you unconditionally, you have not committed the unpardonable sin, and pray to God to help you through this.