The confusion might lie in the fact you haven't told us if you used birth control while you had sex on multiple days.
If you are having unprotected sex, YES you could be pregnant. And if you used a condom, there is a possibility that you could be pregnant, as they could leak, have a hole in them, etc.
Also, when you are submitting a question, it would be great to know how old you are. When you are young, your periods can be irregular just because you're young, not because you're having sex.
To sum up: Wait out the month, then take another pregnancy test. BOTH PARTIES need to use their own birth control. Take control over your body and get on birth control. If you go for birth control pills, TAKE THEM EVERY DAY. Don't mess around with this, unless you feel the need to be a parent.
