URL Crawl errors

Hi guys

Can you help me out?

A couple weeks a go my website was fine. Top rank of Google's first page for my key words. I'm small potatoes, only 800 hits a day but a decent platform to grow. My site is eslwriting.org and it's in the ESL teaching niche.

I made some changes and my pages have almost disappeared from Google.

I changed my theme from Thesis 1.8 to a freeby called Sparkling to be mobile friendly.

I added Yost SEO and stopped using the plugin Google sitemaps.

I changed the home button link on the menu - home used to be a category then I made customized home button.

Since traffic has dried up.

I have not been banned from Google, so that's not an issue.

I resubmitted the sitemap (back to Google sitemap).

Google can't fetch my main page - eslwriting.org but it can fetch specific pages.
Web tools shows over 500 sever errors.
The sitemap analysis shows http 500 errors (20 warnings).

Thanks in advance; I promise to pass on your generosity to strangers that I meet in the future to ensure good will keeps moving.

Cheers

rob
eslwriting.org