If your partner is 'large' it can sometimes cause some inflammation, however, the itching is bewildering- have you switched something in your life recently; a new type of food, scented laundry soap, body wash? Also, if you are using condoms- have you tried different ones to see if that is a possibility or possibly a bad batch of condoms? Also, avoid tight fitting underwear, pants, etc. as it will keep it cooler 'down there' thus leaving less moisture that will simply create more bacteria.. Good luck!
Do you use well lubricated condoms or lubricant? Could be dryness