502 Gateway Error and

My site straightened out yesterday, I ran the tests recommended received “A’s” but today it’s a mess. White pages, need to refresh no 502 Gateway errors. Inside the admin page I need to reload pages and the speed is very, very slow. Example: I changed information for a product, saved, received a white page, reloaded and the page shows links in the far left column but not the actual products admin page, had to refresh a 2nd time and it’s still very slow. Glass Cottage Antiques