Thank you for the additional information.
It sounds like you have gone from someone enjoying personal freedoms and a satisfying life to someone who is overburdened with responsibility. Plus it sounds like you are by nature a mature and responsible person. That is going to go against having to rely on your fiancee's parents for support. You want to be able to support yourself and your family, but you can't right now so inside you may feel like you are letting everyone down, including yourself. That is a tough message to send yourself when you are doing your best.
It is normal to have goals for yourself and want to succeed. And it sounds like you really are satisfied with your relationship. You mentioned being happy and fulfilled with your fiancee. However, when you add
a lot of responsibilities, it can take away that fun part of your life and make it seem like all you do is work, only to have nothing to show for it.
Having your fiancee's mother always being critical of you can add to the already difficult situation you are in. It can also put more pressure on you than you already are putting on yourself. That can make you feel like a failure and make you feel irritable and tired.
Try not to be concerned with what you are feeling. Your response to your situation is very normal, though it doesn't feel so good. What may help is to start changing how you are thinking about your current situation. For one, this is not going to last forever. Having a baby is difficult and very stressful. Add to it the lack of income and work involved, and it is natural to feel this way. But your child will not be young for long and you will not be stuck in your fiancee's parents home either.
Secondly, try to make goals that you want to achieve. Even if you take only small step, you are still working towards those goals.
Thirdly, try to take advantage of the situation by asking your fiancee's parents to take care of your child with you two go out. Even if it's just for a few hours it is worth it. And it gives you something to look forward to.
Fourth, try to find something you can do that you love. Join a baseball league, get together with friends, etc. Bring your fiancee along with the baby if you need to. It helps to get out your stress
and brings you closer as a family.
Finally, talk about your dreams with your fiancee. Even if you cannot do any of those things now, just fantasizing together can help you both feel better and give you ideas of how you want your future to look.
I hope this has helped you,