getting pregnant chances of this

Right so I gave head about 7/8 weeks ago and I may have got some cum on my hand but not visibly. Then I think I went to the loo about 40 mins later. Then I got my period 6 days after (well I thought I did) but it was just really really light and I put a tampon in and when I took it out there was nothing on it (never happened before) and then my period got a tiny bit heavier the next day and the next day after it started properly and was really heavy, but only lasted properly for 5 days. This period only lasted 5/4 days, normally they last 7 and are really heavy but this one was lighter than normal. Is there any way this trip to the loo got be pregnant? No signs really only the period and sore boobs but I always have that.  I've never have sex btw