Dandruff can be provoked by numerous things. For example you may have a predisposition to it, but it is worsened in the winter because of additional drying out of the skin by the cold, dry air. Also, sometimes dandruff can be worsened by become colonized on the skin with certain types of fungus, which could be something you have newly acquired.
I would not worry
about newly having dandruff, therefore, unless there are other accompanying symptoms, such as changes in the texture or moisture of your hair and skin generally on other parts of your body, which could indicate a nutritional problem or a thyroid problem.
First line treatment for dandruff is an over the counter anti dandruff shampoo, so I would recommend starting with that. If that doesn't work, it may be because your dandruff has become quite inflamed and tipped over into a different condition, called seborrheic dermatitis, which causes scaling and itching and redness of the scalp. Treatment of seborrheic dermatitis sometimes requires stronger medications, such as steroid or antifungal lotions or shampoos prescribed by your doctor
I would recommend talking to your primary care doctor
to determine what is going on and what treatments are best for you.