What Causes Delay In Periods With Negative Pregnancy Test?

Hello last month I remeber taking three tri-sprintec pills then just stopped. So last month my period came a day early. My period app said I ovulate on Jan 8 well I had sex in Jan 11 and my fiance came in me I strted my period Jan 19-20 and it also ended two days earlier then usual. So this month my cycle is 3 days late but a negative test. Could I be pregnant? Or body out of whack?