a lot times they put a water flow restricter in the faucets. (are you in Calif?) you cannot buy any non-restrictive flow faucets in the state.

sometimes you can remove the flow restricter gasket. google your faucet and see if you can do it.

If your spray head is separate from your faucet ... that kind of faucet is not supposed to work with a hand held spray head on -- the spray head is supposed to get the water flow instead -- or at least that is how mine works.

If the sprayer head of the faucet is otherwise "restricted", try washing out any grit that might be stuck in the spray head by running water BACKWARDS through it -- from the outside toward the inside of it. You may even need to rub the outside with your finger as you do so to push any grit stuck in it out.

Edited my earlier post.

Do you have a hand held sprayer separate from the faucet or

Do you mean that you have the equivalent of a hand held shower faucet that can either be used in place or lifted out or

Do you just have a faucet and you've unscrewed the end "sprayer"/diffuser piece on the end off of it?

Here is a link for gerber replacement parts.
https://www.gerberparts.com/gerber-kitchen-faucet-parts.htm

There appears to be some "universal" type heads if you can't find gerber. Maybe see if any look the same as yours where the fitting is:

https://www.google.com/search?q=gerber+kitchen+faucet+replacement+spray+head&client=firefox-b-1-d&sxsrf=ACYBGNSbqKubKgkHHLA1u8Fm-LexSVDmuw:1570919056263&source=lnms&tbm=shop&sa=X&ved=0ahUKEwi_3MbC4ZflAhWOFzQIHbxnDwAQ_AUIESgB&biw=840&bih=455