Reply to Microphone feedback help!

Hello I'm sitting here with a problem.
Tomorrow I stream / broadcast - radio out to people . I speake , talking , doing voice-over, ect ... or whatever you call it, with my microphone so I can talk to people , introduce music etc , so it's a little bit more exciting than just mixing music together.

the problem is that when I use the microphone I get feedback through the microphone and speakers , so that people can hear my voice and music in " echo " because of the feedback. How do I fix the problem?

I would still like to be able to "cue" music in my headphones.

How do I make this setup?
- I only hear the music I mix on monitor (no mic voice)
- People need to hear "music + mic ​​sound"
If this setup works, then there should be no feedback in mic / speaker

I have the following gear .

- PC Computer - Win7
- KRK monitor RK 5 G2
- Focusrite Scarlett 2I2 and standard sound card that sits in comuteren .
- Microphone - Red NT1 -A, Shure PG48 - XLR
- Headphones - Beyerdynamic DT-770 Pro 80 ohm and a pair of DJ headphones.
- Dj Software - Virtual DJ 7 and MIXXX
- DAW - Ableton Live 9 standard
- Dj Controller - Numark Mixtrack Pro II with internal sound card

in total there are 3 soundcard (Focusrite, PC, and DJ controller)

hope there is someone out there who has a solution.

Regards, Paul