big server load and database connection

My problem is that my site is growing and growing with visitors, and the last 10 days i have problem with database error connections and also the server load in the server where i am, it is always big and gets lot of resources. i am not running anything of cache plugins, and i am wondering if cache plugins may help me to defence the problem. i am not have problems all the time, but 2-3 times a day for 20 minutes each time, when i have many visitors. CAN you suggest me an wordpress expert or a company, which i can use as support to tweak my site to have more speed ans stability. thanks very much for reading my story.