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Because you took I-pill you got the menses on 7th May and then probably due to hormonal
disturbance which is common with I-pill you got a repeat bleeding on 17-18th May.The next episode of sex looks to be a protected one as you gave your history but still the cycle got delayed the reason for which can be :-
-hormonal imbalance or
which is less possible
To be on a safer side get a urine pregnancy test done after 7th if that is negative please consult a Gynaecologist for opinion and treatment of hormonal problem.Remember you are calculating cycle from 7th May which was bleeding due to I-pill and not your regular periods so please consult a Gynaec.