It could have to do with your faucet; if you live in an area with hard water you may have mineral deposits that are keeping your pressure from being good. It may also be your shut off valve under the sink for the same reason.
My advice is to shut the water off under the sink (have plenty of towels and a mop handy) and take the faucet apart to see if you have stuff gunking up the works. They sell rebuild kits at hardware stores, and if you go someplace like Ace or TrueValue, you can probably find someone that will have knowledge in the subject and give you guidence.
If all else fails, call the plumber.