Hi Donna,
If the water flow coming into the rig is low, you may find that you have to hold the pedal down, partially or fully, for 10-15 seconds to get water flowing. A clogged water filter at your water connection could also cause this.
If you're getting good water flow elsewhere, you may need to remove the inlet valve from the toilet and inspect it for buildup of dirt, calcium buildup, or other crud. If you have a Dometic 310, the valve is at the base, on the right side facing the toilet, at the rear. There may be one or two screws holding the valve in place, along with snap-in-place locking retainers. Of course, the water needs to be turned off before removing the inlet valve.
The anti-siphon valve that goes up from the inlet valve to the top of the toilet at the rear might also need to be inspected for buildup of crud.