i am 20 years old.i had very regular periods till 10th may 2008(27 day cycle).ihave never used any painkillers/birth control pills for them.

On 15th may(while i was still bleeding),i had mutual masturbation with my boyfriend.As far as he remembers,he didn't use the same hand for both our genitals.
I usually bleed heavily the first 2-3 days and the bleeding slowly subsides by day 7.The bleeding which started on 10th may(i was never that highly sexually stimulated before) and continued for 14 days,i.e.,the bleeding seemed to subside after a week but again started the next day as though a fresh cycle had started.

Now it is 11th june(day 33,isn't it?),and i still didn't have my periods.i have absolutely no symptoms.....my breasts are perfectly normal,no bleeding at all,no nausea,i haven't been physically as stressed as last month,not much fatigue....
if i am not pregnant,how come my periods are late by 6 days???....how long is it normal for the periods to be delayed because of the irregular periods last time???...
please help, i have been very anxious as the periods are getting delayed further and further....is it because i am pregnant?... any symptoms should have shown by now,right? (since it is 4 weeks since possible conception)....