could I be pregnant?

last month I bled very light for 2 days on the day i was supposed to get my period. It was brown and then light pink. 9 days later I started bleeding again this time a bit more and lasted 4-5 days like a usual period. a week after I took a pregnancy test, it was negative. My period this month was 6 days late also and a little lighter then usual. I've taken 7 tests all together and all negative. sometimes i feel nauseus but I dont have sore boobs or anything, Could I be stessing myself out by thinking i'm pregnant? or is my cycle changing??? or could it be something else