My period comes every 26 to 28 days, it came on February 15 and not march 15, is that okay?

It could be that I am stressed.

Yeah, I think it's fine really. I'm not an expert but my period is always irregular. I do get scared sometimes though, because my aunt had the same thing and apparently she had endometriosis which scarred her fallopian tubes to the point where she can no longer have children. I would recommend eating some spinach(raw or cooked) or anything else high in iron. I always get irregular when I'm iron deficient and so normally a few days of eating spinach gets me going. If you are irregular paired with HORRIBLE cramps, I'd see a doctor. Stress effects me too but in that case, the only thing you can do is just meditate or something. Find some time to relax.