OMG Help me! 😩

Kirsty
So...I think I'm pregnant. But I need your advice! 
Now I'm currently on day 38 of this cycle. Now getting to 38 days isn't exactly abnormal for me 1 in every 3 or so cycles I hit day 40 before I get my period - that being said my periods are irregular because I do have some cycles that are only 20 days long! But I NEVER EVER miss a period and I always know a couple days before I'm due to start due to symthoms etc.
I decided to start losing some weight so I could get healthier, fit into a bridesmaid dress in August and hopefully get my cycles to being somewhat regular. I've been on this weight loss Journey only 6 weeks and I've lost 1s 1ibs - which I'm increibly proud off. 
But I've been told losing this much weight although not unhealthy can mean that my cycles get even more jumbled than Normal. Despite this however I've been getting pregnancy signs - mild cramps, headaches, on and off tender breasts, appetite changes etc and all that together with a late/missed period... 
I should also mention I've taken a pregnancy test but it registered BFN, that being said it was a strip test and I've had it for ages so I'm not entirely sure how reliable it is.
How do I know if this is pregnany, late period or even a missed period due to my weight loss??
What should I do? Go to the doctors? Take another test? Simply cry? I'm having a melt down here! HELP!!