I also take 75 mcg daily & have been taking it for a year & 4 mos. now. For me, many of my symptoms dissappeared relatively fast (most within 2 months). I am 41, male & had had issues with the "foggy headed", macular degenerative type issue, muscle ache, lethargy, nausea, sensitive to cold, dry skin, insomnia & "carpal tunnel" type hand pain & numbness. I also experienced seasonal depression & sleep deprivation depression. This was my life for 12 years until my family doctor thought to check thyroid. I only go to the doctor about every 3 years before being diagnosed so it took time & a new doctor to figure it out - my old dr wanted to treat me for depression - I wouldn't take anything.
After 2 mos all but the carpal tunnel type symptoms were reduced or gone. I did struggle with nausea the first few weeks of taking the meds though. I also go through periods that my symptoms return & learned from my endo that generic versions can be up to 15% stronger or milder than synthroid - so I am starting the synthroid next month once my current 3 mos supply of levothyroxin is used up. Endo said only some people are sensitive to the generic fluxuation - I am one of them.
Overall - I would not ever go back to my old life. I feel great & sleep well. My eyesite, attitude & depression issues have all been greatly reduced or totally resolved. I did gain weight - I am 5'11'' and did weigh 157lbs - I now weigh 176lbs & am stable at that weight with no change to my already active lifestyle. I wish my doctors had figured this out 10 years ago. Not being a hypochondriac & seldom going to the dr for more than a yearly physical - I simply thought I was normal & everyone felt the way I was except for my seasonal depression - which I blamed on the scars of a very bad childhood.
Only other issue I have had is bouts of impotence - but my testostrone levels have dropped since taking the thyroid supplement.... they think I have a benign tumor on my pituitary gland that is causing it all & we are scheduled for a scan next month. Not an issue for you but for the guys out there taking levo. it may be.
The biggest problem I have had is that once diagnosed & confirmed - my Dr only wants to give me the thyroid replacement therapy & ignore the other issues.... I had to push to get a reference to see the endo.... But finally the ball is rolling...