It sounds like you have one or two problems going on.
First, make sure the WiFi you are accessing through has enough speed for what you are trying to do. If it is a lower speed connection and/or there are multiple devices using it at once, you will have this problem.
Second, you need to clear out your device. Have you cleared out the browsers "Cache" and "History" recently. If you haven't, now is the time to do it. NOTE: Before cleaning them out, make sure you have saved any passwords, log in information, etc., as they can be erased and you don't want to lose them.
Third, do you have a lot of apps running all at the same time? If so, this would cause you grief as well. Make sure you actually "turn off" any apps that could be running...