ฉันไม่ได้ไปโรงเรียนหลายวันแล้ว

Does this sentence mean

"I didn't go to school a few days ago" OR
"I didn't go to school for a few days"

What words should I use for "for a few days" and "a few days ago"?

Thanks in advance guys.

ฉันไม่ได้ไปโรงเรียน(มา)หลายวันแล้ว means: I didn't go to school for a few days already.

ฉันไม่ได้ไปโรงเรียน(เมื่อ)หลายวันที่แล้ว means: I didn't go to school a few days ago.

The words in () can be omitted, but can also be added for clarity.

หลาย for 'a few'?

For หลาย my dictionary has 'many/numerous/several'.

Hmm, I suppose 'several' is close to 'a few'. Sort of.