Hi
I understand your concern.
It is not due to primary complex.
Relax.
Every human being is different from each other.
Their body demand and functions are also different.
So everyone has different capacity to deal with situations.
To increase stamina you have to do workout regularly.
Running and cycling for 30 min is very good exercise to increase endurance power of body.
Healthy diet with rich in protein will help.
Extra protein supplement by milk shake or juice can elevated muscle power.
Consult dietician to make proper
diet plan.
Consult
physiotherapy for exercise plan .
Confidence is big thing and motivated your self.
set your goal and do not compare with any another.
Still have a query then feel free to ask.
Happy to help you.
Thank you.