Cause For Feeling Tired And Dizziness After Giving Birth?

Hi, my name is holly I m a 25 years old mum of twins(7 months) . I am so overly exhausted it s unreal I constantly feel fatigued even after a full nights sleep . I keep having extremely dizzy spells to the point I have to put my sons in their cots because I m scared I will drop them through it . My legs go like jelly and I feel very weak all of the time. I am constantly achy all over my joints which are stiff and grind a lot ,I have a burning sensatIon in my spine quite often which usually is followed by sharp stabbing pains in my chest which worsens when I breathe in, my muscles hurt.. you name it! I even have stopped going out really because even walking round the corner I get short of breath and sometimes palpitations .. I m only 8 stone so not overweight . Every one I know keeps telling me it s because I have the boys and I m a new mum but I honestly didn t even feel this bad when I was up four times a night! I have had bloods done recently checking for thyroid problems but it s come back normal. I suffer with tmj but can t see my locked jaw being the reason for it and I honestly believe something else is going on... Anyway I just need some reassurance that I m not a complete hypercondriac as I can t seem to get any answers from my gp. thanks in advance, ​holly.