I would pull them off and look on the backside inside the threads and see if something hasn't blocked the openings. A little bit of broken loose debris will plug up the strainers on the inside. Vinagre will release any calcium and mineral deposits on the inside of the showerhead. There are strainers and small openings that allow the water be reduced to 1.5 gpm (the new national standards). If you can't fix them, you can always replace them with higher flow shower heads or remove the flow restricter on the inside of the female end.

Good Luck

Raymond VinZant Plumbing Prof.