So I had put off buying any kind of product to clean the sensor on my D7100 because I wasn't expecting to have to do so for a while. The other day I went out with my 18-55mm lens and shot some landscape pictures and when I came home and threw them on Lightroom I noticed there were some weird spots on the sky. I chalked it up to not having cleaned the lens and filter in a while, so I cleaned them off and didn't pick the camera up for a couple of days. I went out the other day again, this time with my 35mm f/1.8 and took some landscape shots around town and came home and discovered the same exact pattern of spots on the images. They're not noticeable unless I'm shooting at f/9 (usually the smallest aperture I go down to) and the blue sky is in the shot. I have ordered some sensor cleaning supplies, but they seem to be backordered and won't be here until May.
Are the spots or stains I'm seeing oil spots, or just dirt on the sensor? Attached find two images (post-processing was done to them which brings out the blemishes more) I took with the 35mm lens (I cleaned it and the filter before going out to shoot these) which, to me, show the apparent problem:
Look at the top left hand side of both images, although you can see some of the spots on the top right in the second picture.