If the pump builds pressure and shuts off while running the shower and a sink, it can build more pressure and flow than you are using. You may just need to turn the pressure switch up from 30/50 to 40/60. And yes there should be a gauge on the tank to show you what the pressure is.
The filter may also be the problem. Either by-pass the filter or just take out the filter element and see how much pressure you have.
Either way there is no reason for a house with a well to have low pressure. You are in control of how much pressure you have. As long as the pump is large enough, you can turn it up to supply as much pressure as you want.
Many people say adding a Cycle Stop Valve to get “constant pressure” gives “city like pressure”. If set up correctly, a house with a well can have much better pressure than any city water system. So the saying should be that city people wish they could have pressure as strong as the “constant pressure” from a well pump with a CSV.