hello. my name is dr waleed. actually it is not possible from the history you have given to reach a diagnosis but i can tell you that you must see a doctor very soon so that he can take a complete history and do a physical examination and then do necessary investigations. in this way it would be possible to reach the diagnosis. From whatever history you have given, i can tell you this. you may possibly be losing too much blood that can make you anemic. Severe anemia can make you breathless and cause you dizziness(light-headedness) but that will not explain the nausea though. Also, if you meant vertigo ie the world spins around by dizziness that would be more alarming though. a benign pituitary tumour can be a possible cause too that cause the nausea,vertigo, and irregular menses. if you have vision problems too, then it can be more likely. A pituitary tumour would not explain not the abdominal pain unless unrelated. another possibility is that you are bleeding into your stomach or intestine (is your stool colour blacK?, if so think of bleeding into stomach or early part of small intestine). it will explain the abdominal pain nausea lightheadedness and breathlessness. Polyarteritis nodosa can explain all these symptoms except the irregular vaginal bleeding. Conclusion: please go to your doctor soon for a full workup