Could I be pregnant?

I thought I was starting to get regular periods since coming off the injection last year but then I had sex with my partner which was exactly four weeks ago. If my periods were regular I’ve missed two periods but I’m not exactly sure if I could class them as regular. I haven’t been tracking ovulation so have no idea if or when I’ve ovulated. I had brown and pink spotting last week and oh my lord I am EXHAUSTED!! If I had sex four weeks ago but I’m irregular and/or ovulated later, could I be in early pregnancy?