What could cause a period to be late?

Last month my cycle was 29 days and a little heavier than usual at first, but otherwise normal. The past couple months I’ve spotted right before getting my period and last month was also the month I didn’t spot for the first time. Now I’m on 34 days of my cycle (4 days late) but I haven’t been on 34-35 days for like 2-3 years now so what could have caused it to be this late now?

Yesterday I did start to feel faint cramps like it was about to start and today I do feel bloated but still nothing. I haven’t been under any stress or anything really. I did have a cold last week not sure if that could effect it