Climax problems...Need Help

I need help. I am a brainstem tumor patient and I take a good amount of meds. I do chemotherapy and take BP meds. I have tried levitra and doesn't work. I can get erection for about 10 minutes and my gf get hers. But I can't climax and my penis gets soft. I need help. I just ordered some male vibrators and flesh light to try so hopefully they will work but my gf is sad that i don't get one. If there is something out there to help me climax and stay hard please let me know. I haven't been able to cum for a while it always goes down. Maybe a spray or pill to help me get one. Thanks.