I installed pressure tank on 12/11. For the past few weeks, water pressure almost stops before pump starts. Can anyone help with this?

Reset your tank pressure. Turn off power, then drain tank by opening a lower level faucet until pressure reaches zero. Now check the pressure at the air valve at the top of the tank. It should be set to 2# below the point at which the pump cuts on. So, for example, if your pump cuts on at 30#, then you would set the pressure at 28#.