Am I suffering from a Mental disorder?

I am a dentistry student and I started hating going to school when i became clinician. I really do not like my course it was my parents who chose this for me but during my first 3 years in school i do good.in fact i get high grades.until 1 day i failed 1 subject and it was my 1st time to fail and do not know how to tell my parents.until i told dad and i saw it in their faces that theyre disappointed.My school sucks that even i work hard in clinic its never enough.I usually work on my own and dont ask from friends or classmates.so when it is my 1st time to handle a patient and do a cavity filling i expect the clinical instructor to teach me but she assumes that i know it and when i ask she gets mad so i got scared approaching teacher.starting that time i got lazy going to school and do my requirements.even i try to force my body i dont know whats wrong with me!maybe im lazy but i wanna finish my school! thats why i googled this laziness if im sick or just over reacting? please help.. is there anything i can do? if there is something wrong to me? like a mental disorder or something, how it can be treated? im so much willing to have this treated if im really sick, i hate being like this. or maybe its all in my mind that im just lazy doing my requirements because i know its not worth it!or maybe im just really lazy. but i dont know because when im just home, i love decorating the house,cooking and doing house chores, so if im lazy i wouldnt try to do these things and just stay in bed the whole day. ahh! if the solution is to change careers i dont think it is possible with my parents. theyre the most close minded person ive ever seen in this world! and to add up again im sorry this is too long. sometimes i shake my head. maybe it is mannerism? but whenever i try to control not to, i feel like my head is heavy. i dont know i cant explain really. do i need to have a check up to a doctor? or i just need to really set my mind to a positive thinking or whatever.. ah thank you so much and i hope i get a response to this. God bless always