time lapse

'Over the last 30 day' suggests to me a time period extending up tp the present. Only a present perfect (have learnt/have been learning seems natural to me.

shushkkathe last 30 days

This expression is ambiguous. It could mean (A) the 30 days that end today; it could mean (B) the final 30 days of a time period already mentioned in the context of your conversation (e.g., the last 30 days of the school year that ended 6 months ago).

During the last 30 days (A) I was learning 15 new English words every day.

Thank you so much for your reply. In order to not be ambiguous I'll specify my point a bit: September,1 through September,30 2015 I learned OR was learning 15 new English words every single day. (but now I don't do it. I just read a book in English without trying to memorize all new words I encounter.) So, during OR over the last 30 days (let's pretend it's October,1 today) I was learning OR learn

shushkkaSo, during OR over the last 30 days (let's pretend it's October,1 today) I was learning OR learned OR used to learn 15 new English words every day OR a day OR per day.

I'd say or write:

Over the last 30 days I learned 15 new English words every day.

CJ

Thank you.