Expresses that in addition to A, there is also B; 'moreover', 'besides', 'not only', 'but also'.
Long explanation:
The A。おまけに B。grammar point is used to express that in addition to the first statement A, there is also the second statement B which often emphasizes the negative aspect or difficulty of the situation. It can be translated as 'moreover', 'besides', 'not only', or 'but also' in English. The formation is used with two sentences, placing おまけに between those two sentences.