Last week I had over 4472 URL's in my sitemap with over 2200 pages indexed. I checked today and I have only 133 pages indexed. Should I be worried? I've added about 75 products to my website and changed some meta tags in the last two weeks and didn't resubmit my sitemap. Could this be part of the problem?

Take it easy.They will appear again unless your site is banned.

There isn't a problem, it's just perfectly normal. Stop doing such pointless things and you'll never notice.

Thanks, How often should I re-submit sitemaps?

Never

I've noticed this fluctuation as well.