As I am 3 weeks late I think I'm pregnant but I took a blood test two days after I had taken the morn after pill does the morn after pill make test negative??

It can alter the results- but if you took the pill it's unlikely your pregnant- if you hadn't ovulated yet when you had sex the pill keeps you from ovulating. If you had and the egg was fertilized, it will keep the egg from implanting itself, thereby giving you an early abortion. When you stress your period will be late. Stop worrying, wait a week, then take another test. I'm sure you're fine. Good luck!