You could use it in English too so long as you add 'ago' on the end. "Since two days" makes no sense in English because "since" refers to a point in time not a duration.

That still doesn't sound natural to me. You could answer 'since when' with 'two days ago', but declaring it as a statement I'd say 'for the last two days' or 'since the day before yesterday'.

You could get away with it in speech since it sounds like 'since.. [thinking] two days ago' and it's acceptable to change construction like that in casual speech, but written it doesn't seem right to me.

Could also be do din tak but that implies you’re about to take off