Could I Be Pregnant with Negative Test Results?

So I have had sex twice in my life ....but at both times it was protected sex like we used condoms ......tho the second time ....it took a short time ...like i lost gas before it was that intense... But like let's after a week or two ...I had my periods..it was a heavy flow with painful cramps and it happened the usual way for me ....then the next month I missed my periods.... Ps..have always had unstable periods from the very start of experiencing them ...so missing my periods that month didn't really scare me But now this month (second month from the time I had sex) I vomited once and I think it was cause of my ulcers ...then I barely excrete.....I don't over pee unless I drink a lot .....I have always over slept even before and I still over sleep .....I have always been lazy but there's a way I feel so weak in my body and I don't know if it's cause I might be pregnant....have done several tests and its always indicating negative results... So now please help me describe what the problem with me might be