Best word for health problems

"Symptoms" is probably the best and simplest word. You might get a more precise answer if you give an example of what you are trying to say.

And use the plural form if there is more than one symptom (both pain and vomiting, for example).

symptomatology

symptomatology: the collective symptoms of a patient or disease

Initial symptomatology includes fever...

When it comes to terms that describe a medical illness it is not good to use words such as:

discomfort, ailment, disorders, complaints and trouble

Affliction is OK. In my humble opinion a better way to describe it would be saying they're or you're unwell or have a medical illness. This way you dont divulge any medical confidentiality.

Its probably best to sayunwell and if people ask "Whats wrong?", clarify with its a medical illness.

If confidentiality isn't relevant simply use painful disease.

Complaints may to lay ears connote whining self-pity, which I suspect is why posters so far have disliked it, but it carries no such connotation in medical usage; and indeed it fits the bill quite nicely, as the patient’s own subjective report of what all is wrong, why medical care is sought.

Use the plural when patient complains of more than one thing, as for instance occasional stuffiness and more persistent loss of the sense of smell (anosmia).