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Since you got periods on 16th of May it may be due to the hormonal
effect of your body and occur during IUI .So this time it was a failure better luck for the next as you have to repeat it in the coming cycle.The question is about the multiple residual follicles which have been there as there was no fertilization.Please discuss the issue with your Infertility
specialist who is supposed to do the IUI for you;he will be the best person to talk about it .Discuss in detail and get another trial of IUI.
All the best.