After all these investigation and test at the clinic, it is very difficult that these syymptoms can be because of pregnancy
Normally first pregnacy is the time when female have the usual symptoms of pregnancy very commonly, so after being pregnant for two times and on third you start these things is very rare.
I think because of absence of periods this time and your anxiety
of being pregnant again is making this more worse. May be there are some other problem which can be causing thses symptoms and you are perceiving it as a sign of pregnancy.
I would suggest you to have a proper diet and rest and try to get over with the thinking of being pregnant again and if the problem is presisitng or worsening than you should consult some physician regarding this situation.
Thanks and take care.