Water Pressure in my House
If you are on city water, it is relatively easy to check the pressure where it enters the house. You can purchase an inexpensive gage and attach it to the first hose bib, that will generally give a reasonable pressure reading. Or you can call the city and ask what pressure is supplied at your tap. Your problem may have nothing to do with pressure, it sounds like you have a low flow problem, which is almost always due to a blockage in the line between the meter and the point where you are not getting flow.
The blockage may be due to a valve jammed shut, debris in the line, clogged aerator at the faucet, or a blockage in the shutoff valve for a fixture. Start by determining pressure at the house, and see if you can get decent flow from a hose bib. Then work your way downstream to find the blockage. Blockage in the hot water heater should not affect the cold water pressure and flow, but would affect the hot water pressure and flow downstream of the heater.
Things are more complex if you have a well and pump, but you did not say what type of system you have.