Is this sensors problem? or is it the lens

Hi everyone!

I'm new here. I have Sony NEX C3 with SEL1855 Lens only from last january.

Few months ago I notice there is a black spot if I took panorama photos in bright condition.

And now I notice the black spot even if I took single picture with bright background (previously I notice it only in panoramic photos)

This is the example panoramic picture:

and this is the single picture:

So what is this black spot? is the sensor dirty or the lens? I wanted to open it and try to clean it by myself, but I dont have the experience and the equipment to do that to try it.

Anybody can suggest anything for this?