Hi-
This error simply means your server can’t response to your request timely.
You have installed 57 plugins on your host and some of them are really heavy (WooCommerce, iThemes Security). This is too much for a shared hosting Specially when you have real visitors!
You’re right about HMWP but you may get the same result by deactivating other heavy plugins.
I suggest deactivating plugins which are not a must for your business. It’s also helpful to use a caching plugin. If none of them work for you this means you need a better hosting plan.