Can you tell me what could cause acne conglobata?

Nobody knows: This is a major mystery of dermatology. The key is that it can be managed, though you'll need a dermatologist. Isotretinoin is the mainstay of therapy. Individual lesions may be injected with glucocorticoids. Antibiotics and glucocorticoids may also be used systemically and there are other treatments. It should be possbile to manage you effectively until it remits, usually after many years.