I am so glad that you posted here, I am in a very similar position. My parents are also Catholic, and their first question after we announced we were expecting was "So when is the wedding?" We were already engaged before we got our BFP, and it was definitely unplanned, though we embrace it completely - I always knew I wanted kids young (I'm 21, FI is 23). So, we decided to go ahead with the wedding, and let me tell you, I am beginning to feel it is more trouble than it is worth. Part of me is still wanting to wait until after LO is born and we are better established. FI has a 3 year old from a previous relationship and his child support is sky high, so we're often left with very little money. But the bills get paid, and we're doing ok.
The guilt I feel every time I spend money on something for the wedding is crazy. I feel like we should be concentrating all our energy and time on this baby, but I know that my wedding is also really important to me. I'm not willing to sacrifice having a wonderful special day and honeymoon because I feel rushed or guilty.
That being said, you need to remember that getting married is entirely YOUR choice, NOT your parents. Having battled my father my whole life over the Catholicism issue, I know exactly how you feel about that. My dad acts like my choice not to become Catholic or raise my child that way is personally insulting to him. This obviously makes me angry because it has nothing to do with him personally, I just do not agree with Catholicism. So I know how hard it is, but when he says hurtful things, I just pretend not to hear him and take it with a grain of salt - he was raised Catholic and it's very important to him.
My advice is to do what you want to do when you are ready to do it. Your wedding is a special, once-in-a-lifetime event, and it's not fair to you to rush it because you feel pressured to do so. If your parents are understanding, hopefully they will come around eventually. I wish you the best of luck and happiness, it is nice to know someone else is in this situation with me!
P.S. Sorry if my post is a little disorganized, I'm definitely ready for bed LOL
ETA: Also, the comments about "OH, so you're getting married because you're pregnant" are BEYOND irritating and insulting. We were picking out rings a month before we got a BFP, and I would not get married just because we're expecting. I have gotten this comment from multiple people, including family members, and it makes me incredibly angry.