How to fix low water pressure in shower?

I have decent water pressure around the house, but my shower is quite low. What bothers me most is that when the shower is running, a lot of water goes down the tub spout. Im guessing there is some sort of interruption between the spout and the shower that sends half of the water back through the spout. How can I fix this myself without investing money. I live in a rental and even though I have told the handyman for the property he dismisses the situation telling me that its normal. What can I do?? Thanks!!