If it is only the shower, it is almost always a clogged showerhead or a failing pressure-balance cartridge in the valve — not your house supply. Soak the head in vinegar first, because that is the free half of the diagnosis.
Do the free test first
Unscrew the showerhead and run the valve with the head off, into a bucket. If the flow is strong, the problem is the head and nothing else. Florida water is hard, and mineral scale closes those little nozzles steadily over a couple of years.
Soak the head overnight in white vinegar — a sandwich bag rubber-banded over it works if you cannot get it off — then poke the nozzles through with a pin and rinse. That fixes most cases for the cost of a bottle of vinegar.
If the flow was weak with the head off
Then it is the valve. In a modern shower that means the pressure-balancing cartridge, a plastic and rubber insert inside the mixing valve whose whole job is to stop you being scalded when someone flushes a toilet. They scale up and stiffen with age, and the symptom is reduced flow, sometimes with temperature that wanders.
Cartridges are inexpensive — typically twenty to sixty dollars — and are a genuine DIY job if you can identify the brand and shut the water off. Moen, Delta and Kohler cartridges all pull differently and some need a puller tool. Take a photo of the trim before you start; the brand is usually stamped on the escutcheon or the cartridge itself.
If pressure dropped everywhere, not just the shower
Different problem, and worth taking more seriously:
- Check the main shutoff and the meter valve are fully open — a partly-closed valve after other work is common
- If you are on a well, check the pressure tank and switch
- Galvanised supply pipe in an older home closes up internally with corrosion over decades
- A sudden whole-house drop with no obvious cause, plus a higher water bill, can mean a slab leak
The one that should get your attention
Pressure loss combined with a warm spot on the floor, the sound of running water when nothing is on, or an unexplained jump in the water bill points at a slab leak. In a Pinellas County home on a concrete slab that is worth a leak-detection call quickly, because the water is going somewhere and it is usually under your foundation.