Have you disabled power management yet?
T to enter terminal.
I would assume your system has the driver already loaded in the kernel, if you are able to establish a network connection and access the net, so lets start with disabling power management first.
If the above wasn't enough to fix it, you can also try these commands which did work for another user on here...
Lets try this in terminal...
sudo iwconfig wlan0 power off
If still not fixed, maybe try this?
sudo apt-get install linux-headers-generic build-essential git
git clone http://github.com/lwfinger/rtlwifi_new.git
sudo make install
Then reboot your system, hope this works.
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