8 DPO BFN

So tested at 7DO and BFN, tested again today and yet again BFN. Been trying for two months (I know, I know, not that long) but my sisters and friends have all fallen pregnant so easily, my sisters both got pregnant within a month and my friend wasn't even trying and it happened the one time they didn't use protection. 
I used OPKs's this month and got a postive for 3 days, BD every night a week before my positive opk and then twice a day on my positive OPK days. On the fourth day I got a negative opk and didn't BD that day or the day after as we were just too tired. I am sure I had EWCM the second day of positive opk. 
I am starting to feel like something must be wrong with me. I am healthy, not overweight, I don't smoke, I rarely drink, I exercise, take folic acid.ive had chlamydia twice before but got treated more or less straight away and I have been off birth control for 3 years now. 
My SO had a fertility test two years ago and he came back all fine (this was before we got together) so now I am thinking it is just me!!!
The only symptoms I have had are sore boobs which I always get close to my period, a headache on and off for 3 days which I never usually have the last two days I've been very gassy with a bit of a bad belly and today I've had a dull ache in my lower tummy. I've been very up and down and everything my SO does lately really irritates me but I don't know if this is just PMS!!!
I know there are people out there who have been trying for much longer and I don't any to
Insult anyone by moaning about something so soon but it is just frustrating when you want something so bad and you just don't think it will ever happen! I watch my niece growing up and see her change every day and now my other sister is pregnant and my friend is about to have a baby and it just feels this isn't going to happen!
Anyone else feel my frustration?