I never heard of a penis head shrinking. If you're masturbating, try not doing that for a month to see if you see any improvement in the look of your penis. Maybe you're damaging your penis head with all the vigorous rubbing.
It's not impossible, its been happening to me for the last 5 years. You'll notice it become "flatter" more than anything. Only advice I can give is lay off for as much as you can to preserve it.
Hi,
From some of your symptoms, it appears like an yeast/parasitic infection. If you have any intestinal problem, like parasites, e coli or candida infection, probably solving that might help you.
Solace