Additionally,

I've been thinking, if someone asks ... <grammatical>
I've always thought that if someone asks ... <grammatical>
I've always been thinking ... <ungrammatical>

always + present perfect
You have always been my friend.

always + past continuous
In the old days, you were always/forever washing that car of yours.

always + present perfect continuous
You have always been washing that car.

In other words, you never stop doing it, not even for a second. But is that true with "I've always been thinking"? Have you been thinking this: "if someone asks ..." every second of every day?

All the best.