Fertility

I'm 23, my fiance and I have been together for about 4 yrs, engaged for a year and a half.. and we have been trying to conceive for months roughly about 4 or 5 and everything we do just doesn't work.. I understand I have hypothyroidism and vitamin D deficiency plus other problems so I take my thyroid meds everyday like I'm supposed to and I have to take prenatals due to my lack of vitamins etc. Idk what I'm doing wrong or what I can do to help with us conceiving. I've been getting into a slight depression because of how long we've been trying and nothings happened.. and everytime I go to the dr. They lecture me on how young I am and it's frustrating to hear a lecture when I'm there to get help and not only concieve but to see if I'm okay.. any ideas to help me? I also don't know if my job has anything to do with it. I'm an overnight stocker so I deal with alot of heavy lifting and things falling on me or me getting hurt...