Started what seemed to be a normal period but it only lasted like 45min and hasn't returned what could cause this?

Too soon: It may be too soon to tell. Normal for bleeding to be intermittant, to come and go, and not be constant. This would be typical. Our cycles are determined by our hormones and our hormones are not released in a steady-state, but rather in waves. Also, there's the mechanical aspect of the shedding of the lining. Sounds normal thus far though.