DS2 is nearly 9 and has ASD with SLD. Over the last six months or so he has changed from a passive, flexible, happy and calm child to one who is frequently oppositional, irritable, sensitive (in a sensory way) and angry. For example, he has just had a meltdown at the swimming pool because
i) it was more crowded than usual
ii) there were some screaming/crying children there
iii) I didnt get dressed quickly enough
iv) I made him go into a cubicle to get changed (we were in Ladies)
v) I didnt have change for the vending machine and had to queue. Using the word 'change' made him think I was going to get changed again (!)
Now all these things might have caused a minor strop before, but he would have recovered quickly/been easily distracted. Now he just loses it - and the losing it carries on for longer and is usually accompanied by hitting amd pinching + screaming. I am unable to control him when he gets like this, which is completely new for me - he has always been 'manageable'.
When he's not being like this he returns to his sweet, happy self, but I can't help feeling that he's unhappy for increasing amounts of time 
Have any of you experienced a similar sudden (or fairly sudden) character/mood change in your children and what do you think were the causes?