Nitrofurantoin is making me sick

Okay so I shall preface this with the fact that I have OCD and I tend to fixate a lot on whether or not I'm doing the right thing to keep me from dying you know? I also have a lot of chronic pain and health issues.

Anyway, I was at the doctor yesterday and I have a UTI (expected, I haven't had one in a few years though) and they prescribed me Nitrofurantoin 100mg every 12 hours. About an hour after taking my first dose (with food) I noticed headache, nausea and overall body aches which is unfortunately not that unusual for me. I went about my normal routines and about an hour after taking my second dose I was SO sick. My stomach hurt so bad I was sure I was going to throw up. I was eventually able to fall asleep, hoping I'd feel better today but I don't and now I'm just scared. I want this infection to go away but I'm scared of doctors and these side effects are extremely scary to me.

My mom who has similar problems to me health wise told me I should try taking this medicine once a day instead of twice, is that okay ? I know Google says to follow your doctors advice but like I said I don't necessarily trust doctors (the one I went to accepts my insurance but aren't the best at explaining things) and I just don't know what to do at all