In English, we do not usually use “the” when talking about time periods, like days or weeks.

Look at these examples:

I went to the shops on Sunday.
Bill flew to San Francisco last Tuesday.
Last week, I saw Mary.
Next year, I’m going to travel to Japan.

See how we never use “the” in these circumstances?  With days, we do use the preposition “on”, but otherwise, we don’t put anything in front.