Bam's 100% right on this one. For any concrete advise we would need a lot more info.
Here's the deal though. For your squats in general if you are lifting heavy for you with limited rest breaks between sets your body will fatigue quickly. If you want your body to be trained for reps then you need to drop some weight and increase the rep intensity and be patient. You need to train your body to handle whatever type of load you want to throw at it and that my friend just plain and simple takes time.