You could be suffering from Balanitis - it is an Inflammation of the glans (head) of the penis. It usually causes redness or a blotchy rash on the glans, sometimes with a discharge. The condition may be itchy or uncomfortable but often feels completely normal.
Balanitis is not sexually transmitted. It results from an overgrowth of organisms, which are normally present on the skin of the glans. The condition most commonly occurs in men who have a foreskin (i.e. have not been circumcised). The environment under the foreskin is warm and moist, and these conditions often favour the growth of the organisms that cause balanitis.
These organisms are especially likely to multiply and cause inflammation if moisture is allowed to persist under the foreskin for a while. This may occur if you have not washed for a couple of days, or sometimes after sexual activity (vaginal, oral etc. - with or without a condom). One common organism associated with balanitis is a yeast known as Candida albicans. Balanitis may occur because of excessive growth of Candida, due to moisture and warmth under the foreskin.
The aim of treatment is to keep the glans and foreskin clean and dry to make it difficult for organisms to grow under the foreskin. Medication (e.g. cream or ointment) is rarely necessary, and is usually less effective than good hygiene measures.
Herpes needs to be ruled out in your case and treatment of your partner also maybe needed if the dermatologist/gynaecologist detect any problem with her.