I agree with racefanone that hiring a plumber is likely to be your best and cheapest option…mainly because I doubt that you have a serious problem based on your description. However, you are likely to waste a lot of time fiddling around with the plumbing. from what you describe, I’d guess that you have a sink diverter faucet and it is clogged with debris. If you really do want to mess with it, you could disconnect the faucet supply lines from the angle stop shut-off valves, then open the valves to check that there is good hot and cold water flow. That will prove that the problem is in the faucet or its supply lines. If the flow from the shut-off valves is bad, you could try cleaning these valves and replacing any washers. If the flow is still bad, then you have a more serious problem with your house pipes (such as calcified galvanized pipe). Unless you have a lot of your own time to waste and have a high threshold for aggravation, hire a plumber to fix the problem. It shouldn’t cost more than $200-300 if all that is needed is faucet/valve replacement. If the problem requires the replacement of the house pipes, you will have a bigger bill to pay.