Can I tell how severe my Hypothyroidism is?

I was diagnosed with hypothyroidism a couple of days ago. I also noted that I have been having symptoms like fatigue, dry skin, trouble concentrating and mental "dullness," for at least 2 yrs. It started to worsen by the end of last year. I don't know any of my readings, only that it was lower than normal. They put my on 50 mcg of Synthroid. I son't think I can blame all my symptoms on my thyroid so it's hard for my to know exactly how long I've had symptoms pertaining to it, since I smoke, have a poor diet and was overweight prior to thyroid problems. I was also tested at 14 or 15 for thyroid and it was normal. All my testing has been done with blood work. I suppose my question is, is there anything serious I should be worried about, I took my first synthroid today, so I'm getting treatment now. I have no other health problems besides already being overweight and problems with blood sugar years ago, I am 21, male.