Just keep trying?

Just finished the tww on our 4th iui (both women so donor sperm which is $$$). We've spent over $12,000 already, had second opinions and switched doctors. Everything is normal, no reason I shouldn't be pregnant. I'm so depressed and scared of hemoraging money. We're at the point where we need to shell out more money for more sorry and I just don't know what to do. I feel like we're throwing away tons of money.