I’ve never felt like this before and I’m not sure what to do. Advice?

On Saturday, I went to a local shelter and adopted a 3 year old cat. She’s very friendly and loving but I don’t feel love when I see her. I get stressed. On Sunday evening is when it first started. I was laying in bed watching Netflix and all of the sudden I just started crying. (I rarely cry so I was really confused). I called my mom and she thought that I was reacting to moving out, living on my own, getting a new job, etc etc. But I have been out of college since May, working at my job since July, and living on my own since October. But at this point had a cat for a day. I thought that going to my bedroom and leaving the cat in the living room would help me sleep and calm down. My cat just mewed (A LOT) and scratched at the door for me to open it. Now, this isn't my first pet, but it is the first pet where I am the one fully responsible for it. I tried to ignore her in order for me to calm down.

The next morning, she woke me up at 7am (I usually sleep until about 7:45am). I know this may not seem like a lot of difference but for me it was a drastic change. I woke up to feed her then left to go to work about 7:30. That day at work I was a mess. I was trying to stay focused but I just got overwhelmed sometimes when I thought about the cat. That evening, I went over for dinner at my parents (normal) and my sister stayed the night with me to maybe help me out a little bit. That night I slept better and the whole day went much smoother for me at work. Then, I again went to have dinner at my parents house. When I was going back home, I started crying again. I messaged my sister and was curious what was wrong. She was thinking that I might be getting anxiety about the cat because I am correlating that to my lack of sleep.

Fast forward to Wednesday night, my sister stays over again. She thinks it will help because she loves the cat and I will get more sleep. But now I am having stomach pain and back pain. I sit at a computer chair all day so I am thinking that my back hurts from the constant sitting. But the stomach pain is intermittent. I am not sure if the stomach pain is actually something wrong with me or when I get anxious about the cat my stomach hurts with it.

I am worried that I am not ready to take care of this cat. I should be happy and love this cat. But being around it makes me think all kinds of things. I feel like I am starting to regret adopting this cat.