People are kind of throwing you random ideas of things this could be, and I don't think doctors really work that way. The initial blood tests should have answered questions on most of the big stuff, that's probably why the doctor is a bit more relaxed now. At the same time, it's not crazy to ask for a thyroid function test or an ANA titre or to think about other autoimmune diseases. One thing I would point out is that sometimes autoimmune diseases take some time to show up in bloodwork or other objective tests. I have Hashimoto's (autoimmune hypothyroid) and my first thyroid function test was normal. I kept having symptoms (some of them similar to yours) and a re-test a year later showed altered thyroid function. This was confirmed by another re-test a couple months later.
Once again, a number of your symptoms are fairly nonspecific. This isn't a criticism of you - it's just how many of these conditions show up. But you do have a few specific things in there that I think you should be trying to follow up on.
The first is the red dots. There is no mental or psychological cause I can think of, that causes little red dots on your skin that don't blanch when you press on them. There is likely a biological cause for these dots. I think it would be fair for you to ask your doctor: what is causing these dots? One thing with the dots, I think it would really be best if your blood was taken WHEN you actually have the dots. The physical process that causes the dots might only be happening when you see the dots, if you see what I mean. Normal bloodwork when there are no red dots, might be because your blood is normal at that time. But something caused the dots. Being seen by a doctor when you actually have the dots, will also confirm that these are a particular type of red dot rather than just, I don't know, heat rash, or something.
The second is the lump on your neck. Has your doctor palpated this lump? I have had neck lumps and been told a few things to distinguish an alarming lump that should be seen by a doctor, from a normal lump that I can ignore. But I'm not a doctor, so I would direct you to your doctor to evaluate this.
The third thing is the weakness and pins and needles in your legs. If you have extreme weakness that makes you unable to stand, or that makes your legs crumple beneath you at times, this affects your ability to do self-care in your daily life. I think this is unlikely to result from "stress" but even if it did, it's something that needs to be followed up on, because you are a young woman who needs to be able to work and go through her daily life.
Same thing for the headache. It's debilitating and prevents you living your normal life. The usual recommendation I've heard as a person with migraine is that any headache that is (a) outside of your own usual pattern (i.e. that is a new pattern for you), or that is (b) the worst headache of your life, or that (c) wakes you from sleep, should be seen by Neurology. It sounds like you have (a) and (b) so if this were me I would push for a Neurology consult. It doesn't necessarily mean you need an MRI or have MS. You could have migraines. But migraines are treatable!
The thing about stress is that stress (mental, physical, viruses, etc) can exacerbate autoimmune diseases and cause flares. So even if your symptoms correlate with stressful events or start after an illness, or come and go, that doesn't mean there isn't a biological cause. On the other hand, doctors are not God and cannot diagnose diseases by magic, so if none of the tests show a clear disease process, you have to decide how much to keep looking. However for now I think you have some specific things to follow up so if those have not yet been investigated then you can at least ask about them.