Asking for an appointment is so difficult

I've been unwell for most of this week. I'll probably be fine but I have health issues and it hard to know if it's just a passing bug or something I need to deal with. I've had numerous infections that I've waited too long to be treated and then needed more treatment or have been left with permanent damage.

I've also had an injury for months.

But I find it so hard to make an appointment to get things seen to.

I used to regularly see a physiotherapist but then one time she cancelled and didn't contact me to rearrange and I've just never managed to contact her again. It's been months, many months, approximately 6... I know she's very nice, I know she was very helpful for many years, I know I'm injured, I know the worst she can say is that I'm discharged and I'll need to see my GP to get referred again. I feel like she should have contacted me if I was meant to see her again and it's wrong for me to contact her. It makes me feel anxious anyway but now I haven't had contacted with her for so long it feels even worse. I feel like it was a way of finally getting rid of me after seeing me for years. I always felt so guilty about needing so much physiotherapy. I also know that the podiatrist I see has said she'll contact her and get back to me but it had now been a month and she hasn't contacted me. So I know the physio is likely to be aware of my injury but at the time I said I was coping with it because this is what I do, I say I'm coping because I feel to guilty and anxious to have an appointment.

I could just call tomorrow and explain everything. Well not everything but everything that's relevant like why I didn't just call up after my cancelled appointment and the fact I'm injured and would appreciate some advice or treatment. But it just feels so scary.

The other option is my GP but they only do on the day appointments which means lying awake anxious all night about the phonecall then having to make a call very early when I'm at my least functioning because it's first thing and I have the whole day to face. It takes me a while to get going in the morning due to health issues and autism issues. I explained to my gp last time that making appointments was hard and they said they were trialling online booking which might suit me better because it takes away needing to make the phone call and anxiously being on hold for ages as everyone is calling in at the same time to try to get one of the limited appointments. So I've looked online and they have none. None at all for anytime in the future. I'm fairly sure they go up 2 weeks in advance so the earliest I'll be able to book one for is 2 weeks but that depends on getting in quick when they put them up and I don't know when that exactly is. I worry that in 2 weeks I'll be better or much worse, I don't like cancelling appointments and if I'm worse then I'll likely be more anxious and find it even harder to go. 

I have an appointment this weekend which I know will involve me receiving treatment for something else that has already been decided. I know, they've assessed the problem and decided on treatment and if that doesn't work then they recommend surgery but I feel like I'm going to turn up and they'll tell me it's not that bad and why am I troubling them by getting treatment. It's completely unrelated to feeling unwell and being injured but it's another example of how I struggle to let myself access medical treatment because I'm so anxious. Not anxious about being treated but anxious that I'm getting it wrong, anxious that I'm seen as a burden, anxious about using too many resources, anxious that I'll be anxious, anxious that I'll struggle to communicate with them... Just anxious!

Does anyone else have any experience or wisdom about overcoming this? I know deep down, I just need to choose gp or physio and call and ask to be seen and take it from there but it's so hard and it plays on my mind so much and it's not just getting the appointment, I then need to actually go to the appointment!