By definition you cannot menstruate and be pregnant at the same time, no. But you can bleed while pregnant. The bleeding can be similar to a period. But a period is the sloughing off of the uterine lining. When you are pregnant the embryo implants into the uterine lining. If you were to have a period while pregnant you would lose your uterine lining and thus lose the baby.
Bleeding while pregnant can be caused by many things. If you are experiencing period-like bleeding and getting negative pregnancy tests you are not pregnant.
It is rare, but there are people who still have their periods while pregnant. As JoyRenee said, if you are having your period and have a negative pregnancy test, you are almost certainly not pregnant. If you have doubts about whether you are pregnant or not, you can have a blood test done. They are more accurate than the urine ones.
Technically you cannot have a "real" period. Many times women will confuse vaginal bleeding with a period cause they can look identical. The main reason you don't have a period while pregnant is because you don't ovulate while pregnant, and ovulation is what triggers a period, not vise versa.
During my first pregnancy I bled from weeks 5-10 almost every day bright red with clots. I would only get cramps When I wasn't bleeding. Never while blood was actively coming out (if that makes sense). I tested positive 2 weeks after unprotected sex and got a positive and even while bleeding that didn't change. From everything you have stated I do not believe you are pregnant. Are you trying to get pregnant? I would really consider what you want. I got pregnant at 19 with my first and it was honestly the hardest thing. Please use protection.
It is possible to have cyclic bleeding while you are pregnant that is not menstrual, and it is possible to be pregnant with negative test results. My mother had cyclic bleeding during all 5 of her pregnancies thru birth, and every pregnancy showed negative on urine and blood testing until she was in her 3rd trimesters. the only way she was able to verify her pregnancies was thru ultrasounds. However, it is always best to go to the doctor if you are pregnant or suspect you are pregnant, and bleeding or spotting occurs, because it could be an indicator that something is wrong. When you are pregnant, never second guess yourself, keep asking questions of your doctor until you are satisfied, be persistent, because no one knows your body like you do.
Also, there are many things that can cause pseudo pregnancies, and the symptoms of pregnancy without actually being pregnant. If you are having symptoms of pregnancy with negative test results, ask for a sonogram or ultrasound. If it shows that you are still not pregnant, your doctor will do further testing to see what is causing your symptoms.
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