Many computers have several sockets, but only one USB PORT. In other words, you may be plugging everything into just one logical connection, even though your computer has several holes you can shove the connector into.
An external USB port expander, especially one with a wall-wart (transformer) to supply power to the USB devices instead of drawing on the computer, usually will do a better job of separating the channels. The packaging may not tell you much about how sophisticated the device is; but generally the powered external add-on ports will include better isolation. In theory, you should be able to connect everything together on one - but it often bogs down.
Most USB devices do draw power from the socket you plug them into, and most computers can only supply a tiny bit of power without bogging down, so an externally powered external USB bridge may help to make sure that all the plugged ins get sufficient juice.
Mixing USB-1 and USB-2 devices generally works okay, although all the devices may get pulled back to USB-1 speed. Better bridges will indicate "automatic speed switching" or some such unintelligible blather that's supposed to mean that they can run mixed devices each at its own proper/best speed.