Hi,
You should avoid using a deodarant directly to your under arm skin, avoid shaving or waxing the area for some time. These could be the cause of your symptoms.
Try to avoid sweat accumulation at the sites and use a powder. Keep the area clean and wear lose, comfortable clothes.
Since when have you noticed the lesion?
This could be some insect bite, eczema or bacterial skin infection or dermatitis.
You could take oral antihistamine medications for the itching and apply calamine lotion at the site.
It would be best to consult a skin specialist as nothing can be said with surety without having a look at the lesions.
Let us know about what the doctor advises and post us if you have any other doubts.
Regards.
I had a similar thing happen and it turned out I am allergic to some deodorant. I can now use about 3 different brands but for a time I could only use something like dove sensitive skin.