Thank you for the question..
Brief...You did not mention your sex and age...If you are male and above 10 years of age,most probably your symptoms can be because of genetic cause.
Detail..
There are some neuromuscular diseases and autoimmune diseases which appear in 2nd or 3rd decade of life.
For example..Duchhenne muscular dystrophy ,or
dermatomyositis (with proximal
muscle weakness)
Dear your symtomps of difficulty stepping upstairs or getting up chairs ,strongly need some tests....
Duchhenne muscular dystrophy...inherited as X-linked recessive condition,incidence..1 in 3500,female carriers usualy asymptomatic.
Diagnosis can be done if there is high plasma
creatinine kinase (more than 5000),
mutation in
dystrophin gene,and muscle biopsy will show dystrophic picture with absent dystrophin....Since this disease also effects respiratory muscle functions so can effect proper mucus clearance...
In girls these type of symptoms highly suggest autoimmune disease, can also be because of other genetic diseases..
But I would also highly recommend you to get your genetic tests done as your doctor said..and discuss further..
Hope my answer would be helpfull for you..
Regards,
Dr.Maheshwari