I had unprotected sex on the 1st march and had period on 11th but only bled 3 days which is unusual for me and have been needing the loo more often and feeling very tired and worn out all the time when I haven't even done anything what are the chances of being pregnant

I'm sorry, but it is impossible to give odds. You can have a light period and be pregnant. All symptoms are indistinguishable from getting your period or being pregnant. Even vomiting can be a totally unrelated problem. There is NO way to know without a test.