The issue related to fasting that who can fast and who can’t fast is very simple.
Those patients who are sick from beginning and their sickness is continue and they are on compulsory medication for them their is exemption.
But if anyone on the basis of doubt wants to drop his fast and just have doubt that if he fasts he might face problem, in this there are two groups:
1- Those who are not strong enough but also not taking any compulsory medicine or if they are taking medicine, can’t change its timing for example diabetic patients who take insulin so they can take it at sahr and Iftar. Otherwise if their condition is not suitable they will be amongst first group ( as Quran says those who sick or on journey can drop his fast and do on other days after the holy month of Ramadan)
2- Now you are in this 2nd group who has doubt that if you fast you might have pain or exertion etc. Therefore in your case you can’t eat and drink from beginning, you have to fast that day and if you feel that you have unbearable condition then you can break your fast. Otherwise there is no reason for you to break your fast at very beginning I mean since morning you can’t.
The last way remains for you that you travel that day out of you city that would be 44 Km going and coming but the city is big like New York, Toronto etc they you must calculate 44 km after the official city boundary according to municipal authorities declared. Then after leaving “Hadd e Tarakhus” ( City Boundary) you can break your Fast and then you can come to your Watan ( your own city) but once you are in your own city you can’t eat and drink as much as you wish rather you can eat and drink as required. And also you have to follow the dignity of the Holy Month or Ramazan( I mean not allowed to eat and drink openly).