Recently my submerged well pump has been running every 4 minutes and then shutting down, I also noticed that water pressure is lower than usual and that the pump runs to keep the pressure at 28-30 psi. Is there a problem with the expansion tank?

One thought is the check valve or foot valve is not working. To check your expansion tank take tap on it starting from the bottom and bang up toward the top. It should change sound about halfway up. If it's the same sound it to full of water and the air is down or bladder shot. The tank needs to be adjusted with pressurized air. In another words the tank pressure (Gage) should be adjusted 2 lb less than what your low pressure switch is set at say low is 20lb and high 40 The tank should be at 18 psi. Check the tank and if it needs air you need an air compressor of pump. Basic for a well pump to go on and off check valve bad crack line losing prime or expansion tank or pressure switch. Start from there

Recently my submerged well pump has been running every 4 minutes and then shutting down, I also noticed that water pressure is lower than usual and that the pump runs to keep the pressure at 28-30 psi. Is there a problem with the expansion tank?

This doesn't sound like a expansion tank problem. I think Boat nailed it with a faulty check/foot valve. Note: If the foot valves at fault and remains open then you can install a check valve up on the surface in the suction line.
Good luck, Tom