to make matters worse; on top of that; what's more
Adds an additional negative or undesirable point to a situation. Often used when listing complaints or unfortunate circumstances.
雨が降ってきた。おまけに傘も忘れた。
It started raining. On top of that, I forgot my umbrella.
彼は遅刻した。おまけに宿題も忘れた。
He was late. What's more, he forgot his homework.