Please reassure me, hypermobility, knee pain

[Mummytron]

Quick history,
Ds1(10) 6 year history of Hypermobility syndrome. Has episodes of knee pain which last a few days and then goes away. This time has been six days and today I took him to A and E because painkillers aren't helping much and I was worried. They put cream on to do bloods but then decided they didn't need to. Now I'm worried I should have pushed incase it's something nasty like leukaemia. He had an X Ray which was fine and is being referred to paediatrics through GP but I've got home and wished I'd insisted about bloods.
Anyone with hypermobility have any advice, is it reasonable for it to flare and last this long? They have given him crutches to support it for a week.
Thanks

I have Ehlers Danlos Classic type as has DD and definitely have either overused, overstretched joints to the point that there is a flare up of pain or something slipping out of place. The amount of time they last depends on what did it in the first place in my experience. DD had one of her worst flare ups (severe pain in the balls of both heels) that I think might have been aggravated by her growth at the times. As neither of us had been diagnosed at the time, we had no idea what the issue was but in hindsight it was brought on by too much walking on holiday. She had problems with it for months. I find that if overuse has caused tendonitis, that can go on for a fair few months too.

It's good that DS has a referral. Hopefully that will establish what has set the pain off and ways to protect his joints in future. The thing that really helps while I'm in the middle of a painful episode (tendonitis in foot from over use of the treadmill at the gym) is wearing a brace. It really seems to 'hold things together' and helps with pain. The ones I like best are by Neo-G. You can get them a bit cheaper online but if you want to check them out in RL, Boots do them.

For now I think resting the joint and crutches is wise for DS. And when he's had it rested a while then it might be worth looking into a supportive brace.

What sport does he do? Has he been advised which exercise is dodgy with hypermobile joints and which is suitable? I don't think a blood test would show much but if you are worried that this episode is going on a while or is different to usual, then I'd not hesitate to ask the GP for a blood test. I hope his referral comes through soon. Knee pain is rotten.

Thank you for your response and sorry for the delay in replying to you.
He didn't seem to do anything this time to aggregate it, but I'm convinced he's growing and also hormonal. Emotions are exaggerated in all ways.
He hurt it six weeks ago but after a week it seemed fine. We are now 9 days in and while it seems to be improving it is by very small measures.
I will look into the knee brace.