I think that there is a problem with your toilet training, quite frankly. You said "Now, I will say my son is very difficult, doesn't like going potty, I spend some nights all my night trying to get him to go on it." That's a bad sign, DB.
Children have so little in their lives that they can control. Everyone tells them what to do, when to do it, and how to do it. The only thing they can control is toileting and eating. And he is controling his toileting. The reason, I believe, is because of the stress that YOU (and maybe your mother) are putting on him.
Boys usually train later than girls. A slew of women on here would tell you that their boys didn't train until they were 3. You shouldn't be spending some night all your night, as you put it, pushing him to go the bathroom. No wonder he is stressed out to the max.
You and your mom need to go to the ped together and learn what TO do and what NOT to do with this child and the potty. You also need to be very honest with the doctor in what has been and is going on. If you don't, your little boy is going to be a mess for a long time. If you don't believe me, ask your ped and he or she will explain.
Yes, I would take your child out of preschool now until you fix what is wrong at home and he can stop stressing out over the toilet.
Dawn