It seems you are having dermatitis
between your legs. This could be secondary to the intertrigo
which is due to the excessive sweating
. Usually this infections are mixed infections, fungal infections or bacterial infections. Mixed and fungal infections flare up with the soap. Using deodorants and scents may worsen the situation.
The same type of the infection could be infecting your naval. The naval hygiene is usually neglected; however is very important.
I will advise you to report to a skin specialist and get the appropriate treatment. I hope this helps you.
Dr. Nishikant Shrotri