Can someone answer this?

I'm going to the doctor this week. But,  basically, I just winged the whole 'TTC' in regards to tracking bbt/opk's etc (don't do either) so I don't know when I ovulated. I am pregnant, I took a FRER on Monday 14th which was clearly positive.. My question is, that is EXACTLY 3 weeks after my last period started. LMP = 23rd June.. How did I get such an early definite result on my hpt? Apparently I am 3w6d today, and only 2w7d when I got my positive. 
​Am I only 3w6d along? (I know a doctor has to confirm but still..) hmm........ Having the worst sore boobs and on off nausea and so tired/fatigued!  

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