Sounds like you have the ol' mysterious often overlooked outside shower head valve OFF and the hot and cold mix in the valves because they are open. So elsewhere in the house, you get luke warm or in the winter, cold water out even though the hot valve at the faucet is on.
That can also happen with the main inside shower. The shut off at the head is set off, but the valve(s) are still on. Some drip, some don't.
So, check those two things. One or both are likely set wrong. Both the shut off in the head, AND the shut off valves below must be off. My inside shower did that to me for a while until I noticed. It has the single handle faucet and I was leaving it on when I shut of the head. And one time 15 years ago that happened with my outside shower.