If the area you are in is significantly hillier than where you were, accompanied by the break from cycling you may just be overdoing it a bit.
Usually seat height pain can be verified both by which side (front/back) of knee is hurting, as well as a change in it with small adjustments.
Without knowing anything else about you, age, health, etc. The first thing I would suggest to you is to raise seat right to highest level that doesn't hurt privates. Drop a bob line off your knee at the "3" O clock postion to check your fore and aft. You basically want the knee to be in line with the ball of your foot/pedal shaft give or take a touch. See that your knee has a slight bend in it at the furthest extension, you don't want it straight.
After that, select gears (if applicable) that allow you to have a higher cadence while climbing or under load. If you are having to 'push' the gears you may be hurting your knee that way as well.