Shampoo or hormones?

Ok, I need your help!  After I became pregnant, my hair became VERY oily.  I switched shampoos (from Pantene to Pert Plus) and that helped.  Now, my hair is doing it again.  I switched back to Pantene from Pert Plus, but that hasn't helped at all.  Will changing to another shampoo help or is this hormones?  How long will it last?  I guess it's good that I don't get out of the house much...looks like I don't wash it.  Gross.