帮忙看看这个句子有没有语法错误

应该是 If my birthday by solar calendar is on a weekday when/on which I have to work
因为A weekday is any of the days of the week except Saturday and Sunday.
再问： my birthday by solar calendar is on a weekday on which I have to work, 这句这样对吗？ 那不就是有两个on了吗？
再答： 第一个 on 是介词短语作表语 第二个 on which 引导的是定语从句 修饰 第一个on 后面的名词 没有什么不妥