98 1.8 passat clicking engine

My passat had an oil change about 2 1/2 months ago. I havent had any problems with an oil leak and this morning while driving to school the oil light turned on and within less than a minute my car completely shut off. I had it towed back to my house and changed the oil filter to see if that would fix the problem but it didnt. When the car is idle the clicking noise is barely audible but once it is in gear it is loud and the light turns right back on. Myguess is that the pump isnt pushing enough oil to sustain pressure in the engine , but I dont know if it is the pump or if something else could be causing this problem. does anybody know what the problem could be and if so an estimate on how much to fix it?