I get a periodic vaginal odour and it is making me feel very uncomfortable and apprehensive about sex as it gets more offensive during?

Very common: What you describe could be an overgrowth of a bacteria that is normally present in the vagina. It is quite common and easy to treat - you need to see your doctor for a definite diagnosis and for treatment.

This is likely BV: Bacterial vaginosis is a shift in vaginal flora that may change your normal ph and allow bacteria to grow in the vaginal canal. Now, this, most of the time is not due to a sexually transmitted disease, but due to an overgrowth of bacteria that normally live in the vagina. During sex, semen has a neutral ph that when mixed with this type of bacteria can release a strong odor. See your gyn for rx.