I am having a quarter life crisis .... feeling really old and wasted at 23 on reevaluating my life, help?

i will be completing 23 this december .... and my age came as a sudden surprise to me as i came home on a vacation this time and people started questioning my age ....when i look back, i feel really disappointed ..... i have always been a loner, not that i hate people or am anti-social but most times, i could never find like-minded people to spend time with .... i had been a pampered brat, a single child and highly temperamental ... my father was always my best friend and after i went to college, its my boyfriend who has taken that place ... that apart, the only feather in my cap is the medical degree i will be completing this year .... well i feel wasted, i can't remember a single time i had fun, i was either too disciplined or too stuck up most times, overtly sensitive or reactive to enjoy jokes with people.... i mean i never learnt to enjoy life.... what if i am going to be a doctor, i feel like i've wasted my youth .... i always postponded my thoughts .... would think a day will come when i grow up into a beautiful young lady and have lots of fun ... well it never happened, maybe i never made any effort, maybe i never gave myself a chance to be happy, didnt make enough efforts to .... the only time i was really happy was last year when i had shrunk myself to a size zero, i looked gorgeous, could really keep up with fashion and was so happy with myself .... well with the schedule and my laziness, i quit exercise and watching what i eat ... i am huge now and that depresses me more .... and whenever i think of getting down to a smaller size, i rebuke myself thinking i am 23, not 16... its for me to be a responsible productive and mature member of the society now, not a teenager wimping over my weight .... everything seems bleak now .... and i know i will be getting married in the next three to four years .... before that i study, work hard .... and then its hubby and kids.... i feel that my life has really really ended now !!! feel really ........ empty