I wouldn't think you need to worry too much, but you should probably get it checked out if it continues. Not that cancer is likely - at 20, the odds are very strongly against it - but the options aren't just cancer or nothing. Many things could cause those symptoms. Most likely, it's something minor like IBS or stress, but it could be something like colitis.

Cancer is highly unlikely. When I was 40, I had rectal bleeding for months on end, weight loss, some loose stools (maybe once a week) and trapped wind and gas and the doctor said that if my mother came in with those symptoms, he'd be concerned about cancer, but that at 40, the odds were "less than 1%" and I'd be "the unluckiest person in the world" if that turned out to be the explanation. You are a lot younger than I was and your symptoms are vaguer, so your odds are probably even lower than mine were.

But whatever it is, it's worth checking out if it continues, both for your peace of mind, assuming it turns out to be something minor, which is likely and also to get any treatment necessary.