T.S.
First, know that you are in my prayers as you deal with the ups and downs of this difficult time. Know also that as long as your thoughts and concerns are of God's will, your decisions that you make along the path to having another baby will reflect this. God doesn't punish us or look down upon us for getting help along the way, if that's what our body needs. I'm Catholic, as well, and I truly believe this. One very wonderful priest once told me that our choices are between ourselves and God. Only He knows what we are going through and will help us make our choices accordingly. It sounds like you're doing great and I hope you have success soon.
I don't have advice for you as much as support in the form of a great, true, "keep the faith" story (sorry, it's a little long!). My best friend just turned 36 this February and had been trying to get pregnant for a year. Frustrated, she went to a fertility doctor and found out that she had less than a 1% chance to getting pregnant. She was devastated, and being Catholic, was concerned how far she should go medically in order to persue her dream. She eventually decided to go on Clomid and tried IUI- she was told her chances were excellent at this point since everything was textbook perfect. The doctor was shocked when it didn't work. My friend was really down at this point and decided to really go forth aggressively and try in-vitro, just once, before giving up. Again, there was bad news. She had a cyst and was going to have to wait a month to try IVF; meanwhile, they'd have to monitor her cyst. Well, a month later they did some routine bloodwork and much to everyone's surprise, she was pregnant. It had happened naturally, even in the midst of all the testing! She's almost 6 months along at this point (she took progesterone and baby aspirin the firt trimester to be safe), doing great, and her due date is actually on her own birthday. We say that it's God reminding us that even though His gifts don't always arrive according to our schedule or to our specifications, He has a plan for us nontheless and is truly amazing and miraculous!
Hang in there and know that others are thinking of you and supporting you as you make these difficult choices. Good luck and prayers for a happy and healthy baby soon!