It was because of a plugin called Easy Social Sharing Buttons version 3.5 I bought from Code Canyon. It is quite feature rich and may slow down your website. I would not say you should avoid it but I would advise you to do an extensive research that your website is running fine on different devices and connections if you are going to use it and similar plugins. ESSB’s stylesheet was 5 times the size of my whole website’s stylesheet and it has many JS files as well. Use Pingdom Tools to find out what is causing your website to be slow just like I did and found out.
