OK my last period was normal. Then a week later days later I had sex and then it started again. 2 periods a week apart. Does anyone have any advice on why?

You may have an irregular cycle. How long was your second period? Depending on that and if the sex was unprotected it could have been implantation bleeding?

When it comes to periods, and consistency/regularity and normalcy of them, there is not much that can be said on it. Our bodies are always changing, and particularly when you are younger. There are so many factors that effect our cycles. Illness, exercise, diet, age, lifestyle,birth control/medication the list goes on and on. Its not uncommon to be irregular. Just keep an eye on things. If it continues to do it, or there are other signs of infection or pain etc, make sure you visit your doctor. Good luck