cking up from School

My son is 5 and has just started school. He has never particularly liked his grandma (dad's mum) and after staying overnight at her house once when he was roughly 3 and a half gets into a panic whenever you mention her name or if she calls on the phone. I have not been able to leave him there, even for a few hours by himself. If we go together he will firstly say that he doesn't want to go in but is fine once we are there.
He started school on the 25th September but only did half days for the first few weeks so I hadto arrange for a friend to pick him up twice as I was at work. The first time he was ok but on the next occasion he clearly wasn't happy that she arrived to pick him up. She said that he didn't speak for a long time and was wiping his face as if he had a cold but I know that he was just trying to hold his tears in.
Grandma turned up, unexpectedly one morning before school to take him there with me as she hadn't been there before.  When Elijah saw it was her, he went into a uncontrollable panic infront of her.  He was tearful and kept asking me over and over again who is picking him up.  I told him several times that I would be getting him and Grandma had only come to take him to school, but it just didnt seem to register, he repeated himself constantly.
That day at school, he had a bad day (the first he has had), the teachers said that he had had a wobbly day and had been really tearful and when they asked what was the matter he said he wanted me.  When I got him that day, the first thing he asked was where is Grandma? and he told me straight away that he had been crying because he was worried that she was going to get him.  I have tried to find out on several occasions why he feels this way but he cannot explain it to me.
Now, he seems to panic constantly.  We went away for a weekend at the half term holiday and he must have asked me at least 20 times, who would be getting him from school? and that he doesnt want Aunty Kira or Grandma to pick him up anymore and he doesn't want to ever stay with them.  He repeats this over and over again and even with my reassurance still continues to do so.  It was the first day back at school today and I recieved a call from the teacher at around 2pm to ask me who was picking him up as he was constantly asking them.  When I got him, he cried again.  He has mentioned the same thing again before going to sleep.
He has other fears too - dogs, his posessions, sleeping by himself (he sleeps with me)
His dad and I split up just before he was 3 and a half so was unsettling for him but recovered well and has regular contact with his dad who comes to our flat to see him usually once a week for a day or two and he seems fine with this so I don't think his issues are related to this, but ofcourse I am not an expert.
I am very concerned about my son and how this constant anxiety is affecting him now and his future.
Please help.
Thank you.

[imanaddict]

Wow! It almost sounds like your little boy is having panic attacks or something. Have you discussed any of this with his pediatrician? Has the Grandma and Aunt ever yelled at him, or has he ever gotten into trouble while in their care? If the answer to that is no, I'd definitely take him to see a Dr about this. It could something as simple as separation anxiety, or it could be something more.