<s>[INST] Hi, I have been using Qlaira birth control since August. I take them at the same time everyday. I had my period at the right time in September but did not get my period in October. I have taken sinus medication (over-the-counter stuff) and have not used an antibiotic at all in the past month. Is this a normal side effect of the Qlaira birth control pills or could I be pregnant? Thanks [/INST] Hello, Absence of the menstrual period can happen as a side effect with the use of oral contraceptives, but, this must be reported immediately to the consultant for further management. Not only antibiotics, but, some other medications like carbamazepine, topiramate, ketoconazole, cimetidine etc., also can affect the pharmacological action of hormones. Also, additional protection is needed in the first couple of months after the use of oral pills to prevent failure. You should exclude pregnancy through the blood test before moving on further. Hope this helps. </s>