Oh hun I am concerned... I cant say I havent been where you are!! I didnt mean to be offensive, and I know how frightened you must be!
Anyway, Ive recently been having some health issues in that department, and without going into detail, the doctors had to be sure I wasnt pregnant before testing... They did a test three days after my period was due (I hadnt had my period at that point and due to health issues I can have a month with three periods, then months without one!!)...When that came back negative, they then did another test 1 week later - this was negative also, and because it was second test and 11 days after my period had been due they were happy the result was correct.
6 days after intercourse is VERY early to be having pregnancy symptoms, but then again if it wasnt a one off relation you could be pregnant from another time before that!
You said youre irregular anyway, so if you dont know where in your cycle you are, my best advice would be to do a test in say, 3 days time... if its negative, do another a week later. You may be best going to see your doctor straight away, as they can do these tests for you, and give you alot of advice. I cant give you advice on what to do if you are pregnant, but as far as I am aware termination in legal up to 24 weeks, so you have plenty of time to seek advice and make a decision, so dont rush into anything - talk it over with people you love and trust, and ideally your partner.