Nexus S 4G (Sprint) is becoming very slow/laggy, always running out of RAM...barely using apps. what is going on?

Hi guys,

I have a Nexus S 4G (Sprint) with Jelly Bean, and over the last few weeks it has become very laggy. I seem to always be running out of RAM. This is with only a few apps running in the background. What is going on? When I type a text message the response is not instant.

The latest apps I have installed are HotelTonight and BandsInTown.

Help!

ps. Yes, I have restarted, and upgraded all apps and system.