What Causes Inconsistencies In Periods?

Hi. so I am concerned about something. so I ended up getting my period 2 weeks before my initial start date (august 15) but it wasn t full blood, I guess it was the old blood being pushed out and was really light. but then about 10 days later I got my period again, this time it was still very light, but it lasted a bit longer length wise but then not really so it was kinda short I have it marked as 3 days. usually my periods last 3-4 days and very little to no blood the 5th day. and then now I feel like my cycle is messed because of this weird period month, I have taken multiple pregnancy tests, in which came out negative. but lately like now (in between my last period to my upcoming period) I bleed a bit. I don t know if its spotting because well the tests ive taken were negative. but the blood is very very little, pinkish not so red, and 1% brown. uh, so, then lately when I go have a drink or a smoke sometime I feel sick. I have read my research and I could be psyching myself out, but I really want possible answers on the whole period menstration situation. oh and ive been pooping more, and semi cramps. thank you