I think you should go back to Sixth Form, I was in a similar boat and really struggled with my A-Levels, I failed AS Maths twice, and just gave up with it in the end... Even if you drop down to two subjects, universities will still accept you. I received an unconditional offer from Derby, and an offer from De Montfort, so go back to school, do two A-Levels, cut your work load down, take a little of the stress off. As long as you contact your unis when you apply, you have a chance of getting in. They understand, they're not robots. But go back, x
P.S. I only have two A-Levels.