I missed my interval for almost 1 & 1/2 months now. Possible lead to aside from pregnancy.?

I already did 2 pregnancy test using a "one step urine pregnancy test" at home beside 2 weeks interval, both showed negative (one line). Before i run to my OB-Gyn, near may be some one out there who can give a hand me with possible reason for my delay. Btw, I am married and have 2 kids already.
Answers:

Heavy Periods?

understanding the eb & flow of your cycles is far-reaching, your cycles are regulated by hormones and hormones are regulated by glands, like the thyroid, the hyperthalumas, the pituatary and the ovaries, respectively of these are affected by different things similar to the hyperthalumas can be affected by emotion such as stress, your diet can also cause an inequity, sickness or disease, over physical training can cause delay or even the loss of period altogether, devour a well in proportion diet, take 30 minute walk at least 4 times a week and be forgiving, you don't mention your age as peri-menopause could be an indication, try not to worry in recent times yet if mother temperament doesn't kick surrounded by after 3 missed cycles some recommend 6 months then see your gyno or if you enjoy other symptoms foul discharge or unusual pain ect next see your gyno right away! best wishes!

Do you get pregant if your have sex during your period?

Stress, strenuous exercise, correct of eating traditions?

Abdominal pain due to first intercourse?

It enormously well could be of late stress that's keeping your period from coming.