Most low-flow shower heads use a rubber restrictor that can be removed, if that's the problem. As suggested, try it without the head to see what the flow is like. There might be a screened washer in there that's clogged, or some other restriction in the current head.
If none of that works, and the flow is not very good without the head, a low-flow head might work better. A massage-type probably won't work if flow is the issue.