Painless neck lump on the side of the neck

Hello, I am looking for potentially similar experiences - or just maybe for reassurance. 

In short: I am in my late thirties, and have a painless lump of ca 2-2,5 cm on the right side of my neck, in the posterior triangle for at least 5 weeks now. Otherwise I am completely fine and healthy. 

Long story: After carrying my son on my shoulders, I had a night when I woke up with a sore neck and shoulder. It got better after massaging. 2 nights later it was again a bit sore, I massaged it and found a painless lump on the side of my neck, in the posterior triangle. It wasn't sore when pushing on it, and didn't go away for 2 weeks, so I went to the GP. They felt it, and said they don't think it has to do with the muscles. Because of the location (it is somehow between the trapezoid muscle and the sternomastoid muscle) and how it feels, they don't think it is a lymph node, but based on the physical examination it is rather a sebaceous cyst. 

In the coming week, however, we both felt with my husband that it grew and became more prominent, so I wanted to go back to the GP. They sent me away saying that they are confident in their diagnosis as a skin cyst. This didn't reassure me, and I got a little bit obsessed with the topic. So a bit more than a week later I asked another GP to have a feel, as my health anxiety spiralled out. They said it might be a cyst but they are not entirely sure - what they feel is that it is quite firm and is attached to the muscle beneath. This is what we (me and my husband) feel as well when we touch it. The second GP didn't think it is a lymph node either which was quite reassuring. They think it is rather something that grew out from the muscle - maybe due to an injury. As it is a painless lump, persisting already for 5 weeks, and it is ca 2-2,5 cm, and they are not entirely confident with the diagnosis, they referred me to the local neck lump clinic yesterday, but said that they are not concerned at all. They will also have a look at my blood. 

I got a confirmation of referral, with the information about the current waiting times for ENT for urgent cases 19 weeks, otherwise 89 weeks. I think, neck lump clinic counts as an urgent referral, but still, many weeks in the limbo. It does look like it is nothing serious - if it is really just the muscle, chances of anything cancerous is extremly low according to my understanding. It is just frustrating that having an ultrasound that would clear it up quickly is still so many weeks ahead. I also feel bad that I insisted following it up when it is probably nothing. I am not sure about the growing anymore - it does and look very different (much bigger) if I am tilting my head, so potentially that is why we felt it is growing? Or maybe it does grow a bit? It has a shape that remind me of the snake having eaten an elephant (or rather an orzo noodle) in the the book "The Little Prince"... 

I am not sure what I looking for - maybe stories about painless neck lumps, especially on the side of the neck? Painless muscle lumps? Reassurance that it is not a bad thing that I followed it up, even if it turns out to be a cyst after all? Or any other comments :)