I disagree. I think you can do all three. In fact, I routinely do all three in my workouts. I just finished up a two week phase where I did that 2 times a week, and squated 2 other days as well. And a couple summers ago I did whole body routines with squats and O-lifts together at least once a week, generally twice. I think it comes down to your conditioning level.
Right now you're just weak. And, as a relative beginner you can handle large quantities of intense work because you haven't yet developed to the level of really frying your CNS doing it.
I suggest working on getting more reps and/or sets at the same weight of snatches/cleans. You don't need to work at the near max level with O-lifts at your level. Stick to 5 reps or so per set and avoid failure like the plague. Work on getting more tolerance to volume and more refined technique. You'll end up being able to add weight eventually because your body will be more coordinated and have a base level of conditioning to the demand placed on it.
As for squats, stick in the 8-10 rep range for the majority of your work. The fact that you drop off in strength so rapidly when adding weight has to do with several things, but the biggest issue is that you're just weak.
Bottom line, you need more volume tolerance. Many coaches have said this: as a relative beginner, getting conditioned to volume leads to more gains in size and strength than lifting at the low rep ranges--this is because you lack the coordination and technique to effectively push heavy weights to great results. Also, your strength qualities are very poorly differentiated--this means that anything you do is going to help your max strength, including high volume stuff.
Says Thibs from "Training for Newbies, Part 2"
I'm assuming through all of this that you have satisfactory form in the O-lifts and squats, but I rather doubt you do. You should work on form above all else, for your health in the future and longevity in lifting.