Gemmy, you say that you have been struggling with such thoughts ever since you were diagnosed. I don't know if you were given medication from that time, too, but if so, you might see if a different medication could be prescribed. Medicines for OCD can cause violent thoughts, but a different medicine may be better tolerated.
In addition the encouragement to read and think about two or three scriptures that speak to you about this matter, and doing this even multiple times a day to get them really into your spirit, fight back spiritually, Don't be passive or give up hope about being free from them. Those thoughts aren't your thoughts; they are temptations. Resist them and replace them with the truth (Scriptures that say differently, I am a new creature in Christ, the blood of Jesus protects me now, and such). Also, cry out to Jesus in the middle of being bombarded with the thoughts.
God has not given us a spirit of fear, but of power, love and self-control. But thanks be to God which always causes us to triumph through Christ Jesus. We have the mind of Christ!
I join with you in prayer for deliverance! (heart)!