I had an ipill (plan B) within 12-15 hrs of having protected sex (just to be super sure) and got light periods 1 week later.  It's the next month now, and I'm 6 days overdue.  I took 2 pregnancy tests, one last night and one this morning, both were negative I'm fairly sure that I'm not pregnant but then why aren't my periods coming?

PS. Here's the COMPLETE detail

I'm a 20 year old female who had sex for the first time:

I took regestrone to delay my periods because I planned to get intimate the same day as my periods. Dosage: 2-3 times a day 3-4 days before period expected date. Last dose was the night before having sex.

Had sex the next night, multiple rounds, but protected every time. Even took an ipill the next afternoon just to be doubly sure and got light periods the next week. Although my periods have always been just for 2 days, these were painful and light both. But I dismissed it thinking it's probably because first I gave myself regestrone then ipill, and it caused hormonal imbalance and therefore the difficulty. 

Also, both, my partner and I, had bad cases of flu and it only got worse for both of us later. Mine in fact turned into a stomach infection and alternate cases of diarrhea and constipation with some nausea but no vomitting. I was quite weak for days but then eventually recovered with medicines like Pentacid, Digene and then the ayurvedic way, Zandu Pancharisht cured me well.

It's the next month now and I'm 6 days overdue. I wouldn't say I've not had back pain, mild nausea, excessive urination etc but that could be because I have migraine issues and I'm quite obese (BMI of 33.8) which also makes me worried if the ipill worked or not. (Ipills are said to not work well over BMI 30) 

I did get 2 pregnancy home tests yesterday. One around 9 pm (dinner around 8 pm) and one around 3 am (had made sure not to drink too much fluids and the urine seemed concentrated enough (yellowish).  Both were completely negative. Not even mild or faint lines.  However, my periods still haven't arrived and I'm completely losing my mind because my mom wants to get me checked for PCOS (ultrasound) and if AT ALL I am somehow pregnant, she'll know and I'm certainly dead then! Also, I've put on significant weight over the past 5 months (4 kgs). 

Please please advise! Is it possible to get a false negative 6 weeks after having sex? If not why aren't my periods coming? What can I do to make them come early?