Hi I Have Not Been Geting My Menses After I

Hi i have not been geting my menses after i gave birth to my fourth child.i stoped using injection for 3month.n den i felt nauses n tired n not well back ache so did test came positive wit faint line.den next day took another test n camw out negative.again after few days took another test n negative.but im havin cramps n was having spottin almost for 3weeks o more.wit cramps.but no severe bleeding.am i pregnant o wat.