3 year old with various symptoms, advice please

Hello, I am just posting for some advice or reassurance, not really sure just feeling confused and worried tbh. My son is 3 years old, for months, maybe year he has had visible node in groin area and swollen nodes in neck area, these aren’t really large, but definitely enlarged and can see the one in his groin when he’s moving certain way and can feel the ones in his neck. Over the last 6 months he has complained of leg pain, more so at night and we thought he had growing pains, around the same time he started complaining of stomach pain and in the last month or so this became daily he was also going through transition to nursery that wasn’t going well so I thought tummy pain maybe him feeling anxious. He has been at the docs multiple times in the last 6 months with various things like molluscum (cleared up after 6 weeks ish), swollen tonsils, a fever, and a fall where he bumped his head and had a mild concussion, a few other minor things, and I have had him in about his tummy pain to GP, each time I mentioned the swollen nodes (I’ve also mentioned these way before at other appointments as he’s had them a while and they kept saying they were probably due to a virus etc and I thought nothing of it and they said kids can just have some).

When I mentioned the tummy pain a few months ago they wouldn’t investigate it because of other things like molluscum or just a general cold and wanted that to be cleared up. So I took him back about a month ago now to GP, explained all the symptoms again and my son was examined, the nodes were still enlarged. Urine tests were all fine. Two weeks later he got bloods taken and that came back that WBC was just slightly low, neutrophils just slightly low, but the lymphocyte was 2, and the doc said it should be between 6-8. He then got referred to paediatric and he is waiting for an appointment which is in a few weeks, in the meantime he had a scan last week and that has come back saying he has enlarged nodes around his abdomen. The doctor explained that she did query mesentric adenitis, but obviously his sore tummy has been going on for months now and he has enlarged nodes elsewhere along with leg pain. He has also in the last month or maybe slightly more complained of having a sore head and has said his head made him wobbly a few times, he also complained of a sore head today. I took him to A&E today after him being really unsettled last night with sore tummy, still complaining of it in the morning and then headache in afternoon so I took him in and they said they had read the notes and paeds referral and can’t do anything because it would be better to wait for his paeds appointment in two weeks. I kind of understand this but I’m also really struggling hearing my wee boy in pain and not being able to help, two more weeks of this feels like such a long time! Can anyone help with information or advice, anything that can put my mind at ease, I am really worrying about something like lymphoma with the symptoms he has and I am finding it hard day to day to stay positive until the appointment. Thank you