Shower doesn't work

I'd like to ask everyone's opinion on this. I went to take a shower this morning and when I turned the valve to send the water to the shower head I hardly had any pressure. This has happened in the past, but turning the valve back to the tub and then back to the shower head always seemed to do the trick. I'm assuming the valve is shot. I checked behind the shower to see if the water was just flowing there instead of the shower head, but it was dry as a bone. Will I need to replace the entire fixture to fix this? The fixture is only about 3 years old.

Also, I've noticed slightly less water pressure throughout my house. Any thoughts on this?

I sounds to me like you have a bad cartridge in the shower valve. Your problem isn't low pressure, it's low flow caused by the cartridge not operating properly. Now knowing the brand, it is difficult to suggest any more, but that's where I'd start looking.

Thanks. I'm also not sure of the brand off the top of my head, but I don't believe it was a very expensive fixture. I'll have to take a look.