It has been getting harder and harder to turn the cold water faucet on and off in the bathroom sink. Do I need a plumber?
Maybe, maybe not, depends on your skill level and determination.
Start by slightly loosening the stem nut, did this cure the problem?
If not, then what is the condition of the valve stem, grimy, rusty, gooey? Turn the water off, remove the valve stem and clean it. Check the packing around the stem, what is its condition, can you clean it or replace it?.
While the valve is out, how is the seal washer looking, time to replace? Replacement washers come in multi-size kits, find one that works and you're good. If the kit has new screws, replace that too. If you can't get the screw loose, then don't mess with it, lest you sheer the head off, necessitating replacement of the stem assembly.
If any of this sounds like it is outside of your abilities, then a plumber is recommended. When you call one, tell them what the problem is and they will likely have the parts on their truck when they arrive, saving you both time and money in the repair of the faucet. You could also be ahead of the game and have a packing/seat kit on hand when he arrives, again, saving you time and money by the plumber not having to make a parts run. Worst case scenario is faucet replacement, again, if you feel this is the direction you'd prefer, then go buy one before you call the plumber, it will save you time and money. :cool: