new to hypothyroidism

I am 45. I have just found out today (7-30) that my thyroid levels came back low and I was being started on synthroid 25MCG. I also just found out last week that I had a heart attack. I am now on Coreg for a rapid heart rate and the heart attack. I have fibromyalgia,spinal bone spurs,bulging disc L5S1,spinal fusion c6c7.I have severe depression at times.I have been told lately that I have been a total _itch! I have NO sex drive. I haven't had a menstral period in 6 months. I have severe hot flashes. I have pain frequently in my arms (esp.left), legs (again,esp. the left), back, neck, and sometimes my jaw. I also have had times throughout the last few years, where I have stabbing pain going through the left side of my head. I go back to the doctor again tomorrow.
How am I supposed to know the difference of these symptoms from the other things I have wrong with me? How am I supposed to know if I am having an adverse reaction? I will ask my doctor tomorrow but so often doctors blow you off and unless they have been there, they don't understand. I get short of breath so bad sometimes that I cannot even finish a 5 or 6 word sentence without taking a breath in the middle of the sentence.
I feel like I am just dying. Like all this pain is telling me my time is almost up. I can't sleep most nights and if I have to turn over at all, it wakes me completely up (and I toss and turn every night). These hot flashes are getting ridiculous!