It depends on the threshold of thinking about sex.
I don't talk about sex much, I don't commonly consider it an important thought when it is brought up, I wouldn't necessarily call it "thinking about". It does not become the forefront of attentive thought every other minute, it rarely does take such a center stage. But at some barely conscious level I believe it comes down to curiosity, the mind's latent draw to just follow every thought process based on the elements it has at it's disposal.
Every other minute doesn't mean sex is more then 0.1% of what has been thought, it just means it is easy to follow a trail of elements back to the aesthetics of a subject (in this case to the human form) or to the mechanics of a subject (in this case of reproduction).
It's sort of like if you tried to discuss games without mentioning the graphics or the developers.
As soon as you look at it you have accepted its graphics and your opinions on them.
By accepting that it is not reality you have accepted a thought of how it was developed.
You can't think about life without it circling back somewhere to the act that creates ours, or use your visual sense without consideration for what things look like. This may be a more infrequent circle if it weren't for the fact the mind resides in just such a vessel and interacts with the counterpart components quite often while possessing a subconscious evolutionary response to perpetuate the species.
Short version: I would say no, I don't "think" a verb implying I pursue such thought anywhere near so often.
But yes it is a latent element of possessing eyesight and the ability to think that no matter what you do, you will in fact see and will in fact think.
What you see and think is entirely of fluctuating nature an encompasses a volume far to large to speculate upon.