Welcome to lybrate, please get your stool tested for eggs of worms. You can take:-
t. Albendazole with ivermectin 1 hs daily for 3 days. Siloderm ointment locally after passing stools.

Stop Mastubation because it will lead to psychatric disturbance in near future and for boils on penis apply siloderm ointment and if necessary contact a nearby doctor

for temporary relief of itching, try these self-care measures:
use a high-quality moisturizing cream on your skin.
Apply an anti-itch cream or lotion to the affected area as prescribed by me
avoid scratching whenever possible.
Apply cool, wet compresses.
Take a lukewarm bath.
Wear smooth-textured, loose cotton clothing. Also, deep breathing techniques help your body relax, which may ease pain. Tension and tightness seep from muscles as they receive a quiet message to rela...more

Yes, if it is in diaper area. Avoid diaper, clean the area with water. Mop it dry, don't rub it with clothes. Apply rashfree or siloderm ointment twice daily for 4-5 days.

Apply homeopathic calendula cream, it's safe and without side effects

Also don't use diapers much, because it's not good for them, and also while wiping, do it with soft cloth
Use cotton nappy for him

You can apply siloderm ointment twice daily locally under supervision of skin specialist.
Avoid scratching.

Keep nappy area dry as far possible
zinc oxide cream (rashfree /siloderm) to be applied 3-4 times a day
recover in 3 -4 days.

Itching like that and possibly you have said that it is in around anus, may be due to two common reason - 1) fungal infestation, 2) threadworm. You may take a) albendazole 400 mg - 1 tab before dinner one night and repeat after 10 days (total 2 tabs). B) apply candid b cream locally twice daily for three weeks.