Woke up one day tp having no water at all so I called a plumber. He told me the pressure switch was bad and so he replaced. Now I get normal pressure for 3 seconds then it drops to a slow trickle. It's a well system if that matters. Any ideas how to solve this without paying this guy my other arm? Thanks.

It's hard to say when we are not on site, but this might help. Your system operates in this fashion. When pressure drops to some preset point (for example, 30# pressure), the switch senses this and closes the contact points to send current to the pump. The pump begins to deliever water to the pressure tank until pressure rise to another preset point (for instance, 50#). Then the switch opens the points and turns the pump off. You can watch this cycle on the pressure gauge. In your case, you have two problems:

1. You seem to have no reserve of water so that you only get normal pressure for a few seconds. Even if the pump was not cutting back on, you should be able to get normal pressure for a minute or two, perhaps a little longer, depending on the size of your pressure tank.
2. When pressure drops, your pump does not seem to be cutting on.

I would suggest this. When you get down to a trickle, take a look at your pressure gauge and see what you have. If pressure is low, below 20 or 30 pounds, then see if your pump has cut on. We need to know that to give further advice.

However, if your pressure is still good on the gauge, say above 30# or so, and I'm going to bet it is, then your problem is going to centered around a blockage somewhere. It could involve a water filter, softener, or shut off valve.

The main thing is this. Check that pressure gauge when you are using water and see what it reads.

I happened to catch it hit 30 while it was at a trickle and the pump came on and went to 50 but, there was no change in water pressure at all. The system bypasses the water filter/softener. Why would I have no reserve? Could it be too much air intank

As you watch the system pump up to 50#, that should be a slow, gradual climb, tanking a minute or two or even longer. Is that what you observed? If so, then your system would seem to be fine. If not, then you could have a waterlogged tank, though I think it unlikely in your case. But it is easy to check. Depress the little air valve at the top of the tank for a few seconds. If water comes out, then your tank is bad.

The pressure in your tank should be set, in your case, to 28#. Do this with the system off and pressure drained down to around zero by opening a low level faucet and letting water run.

I think you have an obstruction somewhere. Not too uncommon when a system is worked on for some "crud" to break free in a pipe and move forward until it hits a valve, filter, whatever, and then lodge there. So, it becomes like having a very small diameter pipe at that spot. You turn on water and everything is fine for a second or two, but then pressure drops because the clogged area is only letting a small volume of water through. So, I would check shut off valves, filters, softeners, and anything else that would tend to catch trash.

Ev, do keep us up on events. It's always interesting for us to see how a situation is resolved.

I will keep you posted, and thank you for the info so far.
But when I saw the pressure climb it was actually rapid, about a sec from 30 to 50.

Check your pressure tank in the manner I described above.