I believe that your girlfriend is correct that she is not, and has not been pregnant. It sounds like she has a fairly typical case of Polycystic Ovary Syndrome PCOS (does not always involve cysts on ovaries -- dumb name)
In fact, it may be difficult for her to conceive when she does want to since her periods are irregular.
The medication that she takes to regulate her periods is probably Provera or Medroxyprogesterone Acetate. This medication will cause bleeding (sometimes heavy with clots) if the woman is not pregnant, and will not cause bleeding if she is pregnant -- it will not cause miscarriage.
It is a good idea to use condoms whenever beginning a new relationship.
Another form of birth control that your girlfriend might really like is the oral contraceptive pill. This would regulate her cycles and prevent that heavy bleeding and cramping that you describe.
> Last week she had a bad case of wisdom tooth pain which subsided in about 2 days after taking antibiotic and painkiller.
> Last night 14th may, she experienced a burning sensation around navel which stopped in a couple of hours.
She is pretty sure that she is in no way pregnant, but I have read on the net that many women had periods while being pregnant and that many didn't have any usual pregnancy symptoms during pregnancy. Please advise.
To me it sounds like she might have been pregnant, and had a misscarriage. I got pregnant in November of 2011, I had an ultrasound to confirm and everything was fine. But since the beggining I had low progesteron level. And it never raised, which ended up in me having a misscarriage. It was bad bad horrid cramps with a bad backaque and heavy bleeding, lots of blood came out and I passed a clot also, which was my baby. It was.the worst feeling you could ever have. I had my period the very next month and I bled very heavily and had bad backpain. Has she went to the Dr to get checked?
I had periods the first several months of my pregnancy. I have also been on pills to regulate periods. I would say more of what that sounds like is not pregnancy at all. It sounds like maybe her body is sensative to the pills. I used to produce pregnancy like symptoms when I was on them. I would even have morning sickness. If she has taken a pregnancy test and it came back negative, I would say she is not. Plus, its hard to get pregnant without actually ejaculating inside the vagina. I hope that helps.