I don't only eat much but also drink much 和I not only eat much but also drink much 哪句正确

第二句正确。第一句正确的写法应为：I do not only eat much but also drink much.其中的"do"应是起强调作用。
如果改为否定句“我既不吃太多，也不喝太多。”的意思的话，应是：I neither eat much nor drink much.

都很别扭啊

当然第一句

都不好！