How often should I ask for a priesthood blessing? Every time I feel sick, or uncomfortable, or unsure?

President Franklin D. Richards, of the First Quorum of the Seventy

The answer to this question is basically covered in the Melchizedek Priesthood Handbook wherein it is stated:

“On special occasions Melchizedek Priesthood leaders, bishops, fathers (for their families), and others holding the Melchizedek Priesthood may, on their own initiative or when called upon, give special blessings of comfort and counsel as circumstances suggest. Situations that may be cause for such blessings are:

“A time of stress or trial, of mental, emotional or physical difficulty, such as when there has been a death in the family, or when a person is preparing to be hospitalized for an operation.

“If there is illness, the blessing may be part of the ordinance of administration to the sick; otherwise, it may be a blessing of comfort.

“There are instances when individuals should work out their problems without a special priesthood blessing. No clearly defined rule can be made to designate what to do in every instance except to seek inspiration from the Lord” (see Melchizedek Priesthood Handbook, p. 25).

I would also suggest that your home teacher, quorum leader, or bishop could give additional counsel in special instances.