Mouth lesions located at the upper palate and other parts of oral cavity, in form of blisters, can be a symptom of reccurent infection with herpes simplex virus (the one that causes cold sores at the lips).
Since the herpes virus stays dormant for lifelong in certain skin and/or mucosa areas, the herpes blisters, sores can reoccur at least 2-3 times a year after the initial presentation of the infection.
Another possible diagnosis is an autoimmune disease (your own immune system attacks parts of your own body), known as pemphygoid.
It is a chronic autoimmune inflammatory disease characterized by bubbles in mucous membranes and, occasionally on the skin.
Usually affects older people, but, young males aren't an exception.
Consult a dermatologist about pemphygoid diagnosis!
Best wishes!
Marija