DH not getting job done

Or even started! Last night was an important day on the calendar and we needed to bd. He couldn't even get it up fully! He kept trying and I finally told him to stop. I cried afterwards. It was so depressing. I'm taking medication to help us get pregnant and he can't get it up?! I'm trying to be a supportive wife but honestly I'm feeling some type of way. I can't imagine what else I can do, I've tried it all (except the dirty dirty 50 shades type of crap) and nothing seems to help. Is there a polite way of suggesting viagra? I just don't think I can continue this way.