period late, feel bloated with slight abdominal pain...negative test...help!?

[kit088]

Hi, I am 20 years old and healthy with no major lifestyle changes recently that i can think of. My period has never been 100% regular and to be honest I don't pay much attention to dates but i knew I should have started somewhere around the 25-28th of june, yesterday I took a digital pregnancy test which claims to be 99% accurate which was negative. I have had protected sex 3 times this month (condoms, which didn't split or anything) so surely the chance of being pregnant AND having a false negative is pretty slim?
I have been feeling gassy and bloated with a bit of pain in my gut (like constipation)-which i often get during my period, also have noticed a lot of discharge...which again could be normal i am just worried and reading too much into things!
Should I be very worried? How long should I leave before doing another test/visiting a doctor? should I tell my mom?