Definitely see your doctor, but the odds are probably low that it is cancer. It could probably be a whole load of things.

I am...well, 41 now, but it was a few months back, so I was 40 and had rectal bleeding, again just on the toilet paper and some other symptoms (trapped wind, occasional loose stools, some weight loss). I was referred to a specialist who said that at our age, the odds of colon cancer was extremely low and would be the last thing on his list, although it did have to be considered with those symptoms, that the most likely option was piles but there was also a chance of IBD.

He performed a colonoscopy and sure enough, all that was found was piles.

Best of luck. Hopefully, it will just be something like a side effect of the antibiotics or piles or something equally minor. I think you would have to be very unlucky to get both covid and cancer at the same time. But it should be checked out, to find out what is going on.