I Am A 42 Year Old Type 1 Diabetic And

I am a 42 year old type 1 diabetic and have been a diabetic since I was 12 years old. I have an issue with my sex life, I am happily married for 14 years with two beautiful boys. I have tried Viagra 50mg and 100mg, Cialis and also herbal things and just in the past year I have a problem with staying erect during intercourse, one other huge problem I have had for many years is that I prematurely ejaculate never lasting long and I have tried many herbal things for this as well. My wife and I do not have sex a lot but mostly once sometimes twice a week. I think if I could stay erect and not ejaculate so fast maybe she would enjoy it more often since now it has slacked off. I am not sure if this is a diabetic issue or a stress issue, I am also taking blood pressure medication and my blood pressure is perfect, my diabetic specialist has checked my testosterone levels and my thyroids and he tells me everything is great. I just need to do something and Viagra and Cialis is just way too expensive. Can you recommend something.

Thanks