Skin problems are common, especially in the the pubic area. Even if this is not a sexually transmitted disease this still requires medical attention. I would strongly encourage you to see your primary doctor
to have this evaluated. If you have specific concerns, a dermatologist
or skin specialist can be of help.
There are many sexually transmitted disease that can appear as you describe. Keep in mind many of these such as herpes does not require penis to vagina sexual contact to be transmitted. Oral or anal sex or even non-penetrating contacting can result in transmission.
There are other conditions that can causes a similar appearance. Firstly, folliculitis is a condition that results from inflammation of the hair beds. This is common in the pubic area which is a warm and moist area. This is often caused by a bacterial infection and can be treated with antibiotics. Another concern could be an allergic reaction. Hives can appear as you describe and can be to detergents or fragrances that you use. Hidradenitis suppurtiva is another condition which is caused by inflammation of the sweat glands. There are many other skin conditions like psoriasis
that can start only in the pubic area.
See your doctor. Good luck!