It's possible some debris or dust has entered your print head and is clogging the nozzle. To clear it, heat up the head to 230-270 degrees and let it settle, then re-set the temperature to the glass transition temperature of PLA: about 70 degrees, although you may need to play with it to get the best results. Wait for the temperature to settle, then pull the filament out of the print head. If you have the temperature right, you should see what looks like a straw at the end of the filament, plus any debris it pulled out of the head. Rinse and repeat as necessary and perform on a regular basis.
