I can't imagine any doctor telling you to lose weight.. that's totally insane; I am 5' tall - 61 yrs old, and I weighed 85 lbs once when I was 46 yrs old and very ill -- looked and felt like cr*p........ Why would he tell you to lose weight?? I'm thinking you need a new doctor............ do not lose weight; you will end up wasting away to nothing...... in fact, I think you should gain at least 10 - 15 pounds; you'd probably feel better.............
I mean, it always depends on the person but by your stats I'd say your BMI is actually on the low side.