Site is still slow after Hummingbird optimization and upgrade to VPS hosting

Here's some background on the situation:
I built the site using Upfront. I am using Woocommerce too. There are a number of custom scripts running. And I have optimized the site as much as possible and is running on a VPS but it still seems much slower than it should be. I'm looking for advice on why the site is still slow. There are some pendings on the minification also. Please note, using a CDN to speed up content loading makes the front disappear.