Hi I Had My Period On Jan 11th-15th Had Sex

hi I had my period on jan 11th-15th had sex the 14th and 21st then had midcycle bleeding the 26th-5th my period was due the 4th of feb but stopped bleeding the 5th I took several test but all were negative the last one I took was on the 3rd could I be pregnant or could I just not be having a regular period due to long mid cycle bleeding.