The previous poster's right about grower vs. shower. Don't worry about the size of your flaccid penis. It doesn't matter if it's smaller flaccid. That's normal. (Hyperthyroidism might have been making the flaccid size bigger than usual, and now it's back to normal.)
It also sounds like your dry skin might just need some moisturizer. (But it seems like you probably would have thought of that already.)
It also sounds like it might be a yeast issue. Yeast can cause the skin to crack like you describe, and sex is one of the most common ways to get yeast. If it is just a minor yeast skin infection, cranberry really helps fight yeast (and it's a bit useful for preventing genital infections/UTIs too). If it's yeast, it helps to wash off the penis after sex before going to sleep. Leaving sexual residues on the penis (even just saliva) makes it more likely to develop issues like this.
Hi JT, first a little education for you, there are growers and showers, it works like this, 2 guys both have an erect size of 6 inchs, when slack one has 5 inchs shower, and the other has 2 inchs grower, and sorry but that is how it works in life.
So your skin there are lots of things on the market but keep away from products that will thin your skin, try looking at the Neutrgenar creams there very good, have a look on there site to see if the make anything that you fill will meet your require ments, if not contact them with your problem, and all the facts, its not the time to get embarrassed as you are looking for help.
Good Luck