When I got my first AZ shot I had terrible side effects. Felt like I had COVID and went to the emerg and was tested but came back negative. This was while I was working as a COVID Case Manager for the Public Health Department and I had to take off one week from work it was so bad. Second shot wasn't as bad but still I took off three days after that one. I also prepared myself by taking Tylenol before hand and made sure I had the days off to rest.

Everyone reacts differently. My wife who did the same AZ shots as me didn't feel a thing and was fine.

To the OP, it would be prudent to get tested for COVID since it is your first shot, just to rule it out. In my role, I talked to many people who got COVID after their first shot or within a week of getting the second shot. I hope you start feeling better soon.