Late period

My period is now 16 days late, I have very regular periods so could I have just skipped a period, my s/o and I have been trying to conceive for about two years now but I’ve taken three pregnancy test and they were all negative, 1 a day before expected period 2 four days after missed period 3 about fourteen days after missed period, has anyone had this ? Can something be wrong ? Has anyone had a negative test for so long but also been pregnant?

Also I have noticed some lower back discomfort, I always want to have sex I get some acid reflux but other than that nothing, I smoke cigs and last night I got really wasted but neither have made me throw up which I feel if I was I would’ve gotten sick by now