Elizabeth, have you considered seeing a dietitian to see if there are any ways where you can tweak your diet to make it easier on you? Dieting is great and eating healthily is massive for mental health but it takes time and effort to do so. A dietitian may have some tips where it makes it easier.
With the exercise, are you being to stressful on yourself? As in are you pushing harder than what you need to do? Exercise should be enjoyable. For example, I used to push myself pretty hard but now i just do my 5km every morning at a leisurely pace. I have nothing to prove to anyone and not impressing anyone. I have found that, that is ideal for me. Gives me my 25 mins of exercise i want per day. It might also be worthwhile to seek out some personal trainer, a good one, to refine your exercise to match what you want. I have a mate who is a PT and he sees so many people doing the incorrect types of exercises for what they are trying to achieve. Not saying that you are doing the incorrect types, but it would be good to know that you are doing it right.
Are you practicing mindfulness? If not, I would well recommend that you start doing it. There are some great apps out there for help you. I use "Smiling Mind" daily and after persisting with it, I am now a lot more calm than what i was.
I would think it is pretty normal to get anxious when more tests are ordered but at the same time, you need to keep that anxiety in control. I used to think that if i sneezed, I had cancer as I catastrophised that much. It was the mindfulness that keeps that in check. I still do it to a degree but I am now able to calm myself down.
Great work getting back on here and posting. Understanding why you went off and well done for recognising that.
Keep posting and see if can help guide you through this journey of yours.