why is my Lg G3 phone browsing very slow when am using my mobile data?

[fam_vic]

I notice that my phone brows very slow and when I send message on whatsup messenger it shows the clock sign and up to 20minutes to mark sent I on and of the phone no changes and called the service provider and they send configurations and I install the same problem at time at the bottom on my browser page it shows not connected to internet connect and try again.................so I did factory reset and when I restored the phone all my , pictures and video was all done and still having the same problem but called the service provider and they keep telling me that my SIM shows on their computer that is active that the problem might be from my phone so I put the SIM card in another phone and it was working well and I share the network and connect my Lg g3 phone and it works well on Wi-Fi..............and I have did all settings and reset my phone still the same but I notice that when I open some apps and don't close it even if I take of the battery from the phone and put it on again when I check my taxt or dual window does app are still there..........pls I really need help

 

[Rukbat]

First, when you're done using an app, press the Back button, not the Home button. Pressing Home leaves the app still running, which slows the phone down.

Second, please be more clear. On wifi everything works okay but on mobile data everything is slow? If you take the battery out, then put it in and turn the phone on, then browse to a site - without doing anything else, is it normal or slow?