If you are using a Wi-Fi hotspot (ie wireless Internet), maybe your neighbours' WiFi channels are interfering with yours. If so, try to place your hotspot in an upstairs room nearest your provider's server source.
To optimize channels use the free program inSSIDer to find out the channel with the least interference and then change your WiFi channel accordingly. I find I need to change channels at different times of the day.
I also use the free app Speed Test to see what kind of upload and download speeds I am getting from my provider.
Hope this helps.