What could be the cause of an itchy vagina after intercourse and could you suggest solutions?

I have been to embarrassed to ask this all day but finally decided I wanted opinions from others to establish if this is potentially normal.

After intercourse with my boyfriend, I find that I get itchy the next day or even day after.

We have both been tested and am certain it is not a result of STD’s.

I have been told that it is possible that I may be allergic to his, ahem, ‘liquids’ but don’t know how accurate this is.

I wash afterwards, wear cotton underwear and am quite certain it isn’t thrush.

Do other females find that this is a reoccurring issue and quite normal or could I be allergic to him? Are there other possibilities which escape me?

I have asked my doctor and she has completed tests but has not provided me with an explanation.

PS: Vagisil is my saviour.