I have been suffering from a range of problems, my GP says it is mental, need second opinion?

For the last few years I have been suffering from a range of problems. Mostly mental things like brain fog, confusion, inability to focus and think straight. Also a lot of muscle aches and weakness. I find it particularly hard to walk up and down stairs because my legs and lower back seem weak and wobbly and I have difficultly balancing/controlling movement. I also often drop things especially when feeling particularly weak. I am lethargic, shaky and sometimes get a tightness in chest/restrictive feeling in throat. This seems strange for someone who is relatively young, fit and healthy. I recently got blood test results from my GP who tells me it is all in my head since nothing is showing up in blood tests. I have had full blood count, iron, b12, glucose, liver function, thyroid function, CRP and ESR. All are normal. I had slightly low vit D about 6 months ago despite being the outdoorsy type but I have been having a D3 supplement since then to treat that. Is there anything else that could be wrong with me that wouldn’t be showing up on these tests? I will be looking for a new GP soon but I need to know what sort of things to ask them. I really feel that there is something seriously wrong. Surely a 30 year old woman should not be such a physical and mental cripple! I also often get things like coughing up greenish grey sticky gunk in the mornings and pustules on face and in hair and shoulder and bottom. It seems like at least once a month I get swollen lymph nodes and am also prone to abscesses under arms and in groin area. These aren’t as worrisome as other symptoms but I am just generally pale, weak, tired and unwell!

