Though it is unlikely given the timing you described, you are playing with fire. If you don't want a baby, do not have unprotected intercourse. Regardless of the time of the month.
ditto to christies comment. You should not have unprotected sex if you do not want to have a child. Also the timing does not fit so I do not think there is a chance og you being pregnant
remember that sperm can live 3-7 days instead of you, given the timing it probably isnt very likely, but still. If you choose to engage in unprotected sex, at least be on the birth control pill. but you should always wear condoms just to be safe, especially if your partner has been with others and hasnt been tested.