is this sentence In right form ?

Neither of those is correct. I think you may mean this:

"I have been waiting for your questions for some days / several days / a number of days."

"since" needs to be followed by a specific time reference or specific event. For example, "I have been waiting since Tuesday / since 10 o'clock / etc.", "It has been several days since I asked you for the questions", "It has been three

A is incorrect. B would mean I was waiting for your questions several days ago, but I have not waited for them since.
Did you mean "I have been waiting for your questions for several days"?

It has been some days is normally followed by a mention of something that happened in the past, or has not happened since some

Blue JayB would mean I was waiting for your questions several days ago, but I have not waited for them since.

Sorry, yes, you're right. Rather than saying it was not correct, I guess I should have said it had an unusual meaning that probably wasn't the intended one.

I started to say it was incorrect, then realized it does have a meaning, even though it's not something anyone is likely to say.

Then don't we use following structure ?!

Perfect tense + since + past continuous

Do we always add a specific time happened in the past just right after "since" and not continuous it till now or something ?

And what about this one :

It has been some days since I back to check up your PMs

Blue JayA is incorrect. B would mean I was waiting for your questions several days ago, but I have not waited for them since.Did you mean "I have been waiting for your questions for several days"?It has been some days is normally followed by a mention of something that happened in the past, or has not happened since some poin

19216801Then don't we use following structure ?! Perfect tense + since + past continuous Do we always add a specific time happened in the past just right after "since" and not continuous it till now or something ?

It is rare because the durational activity (the continuous action) must approach a point in time as conceived. Contexts like this are possible:

19216801Yes I intended to use by " it's been ...' instead of "I've been waiting for ..." how it can be expressed in the "it's been .." form or formula or anything it's called ?!!?!?

I'm not sure there's any way. "It's been several days that I've been waiting for your questions" is less wrong than "since", and some people might say it, but it doesn't see