Help many problems

Hi! I recently got into building a quadcopter and I’m very new, so some of my questions may seem obvious, but I honestly can’t figure this out. I am using the APM 2.5, the 3DR compass/gps, and the 3DR telemetry kit. Here are my problems.
Whenever I connect my quad to the mission planner software, the setup prompt comes up. Is it not remembering my previous set up attempts?
I’m having a hard time arming the quad. I hold the left stick in the bottom right position for about 5 seconds, and only about 10% of the time does it actually arm. Sometimes, it helps to press the reset button on the APM.
The quad is very, very wobbly when I manage to arm it and get it off the ground. Usually, it manages to flip itself over and crash in seconds.
The throttle cuts in and out. If I have the throttle at 10%, it jumps between 0% and 10% erratically. I’m not sure, but this seems like a radio problem. However, I’m standing 15 feet away, so something would have to be damaged for the signal to be that weak.
Last but not least, there was this one time when I managed to get it flying without wobbling and flipping, (don’t ask me how, I have no idea) and it had a strong tendency to go in one direction. If everything else gets fixed, I still can’t fly it if it doesn’t hover relatively well.
Thank you for listening to all my problems, and I hope you are kind enough to help me through this.

Ok, first off, for the throttle issues, have you calibrated your esc’s ? There is an explanation on this. Would be my first place to look. As far as the arming issue, when using GPS it will not arm unless you have a solid GPS lock. You can see if that is the problem by having the prearm check bypass the GPS Check. I do not recommend trying to fly that way however, I have had issue when it gets GPS lock it flies away hard on me. The wobbling could be several different things, usually caused by PID settings. Have you done any tunings at all ? What mode are you trying to hover in? I found most defaults work well enough to get it off the ground, however they need tuning to each frame tyoe. the PID’s might be to high causing the wobbling or oscillating you notice. The drifting to one direction could also indicate an esc not calibrated or that you need to trim the copter a bit as well. There are several ways to fix the drift, but I would fix the random throttle problem first and foremost. Try calibrating your ESC’s either thru the APM or one at a time the manual way.