hi Nina, Thank you for posting your Query in Health Care Magic, i understand your concern. The levocetrizine tablet that you are taking for allergy purposes has nothing to do with your menstrual cycle. But if your expected date for menstrual cycle was 20th December, its better you get the pregnancy test done now. And about your question on pregnancy and the drug you are taking, its not advisable to continue the drug once you get pregnant. The levocetrizine drug has bad effects on your baby as it can cause birth defects, so i advice you to discontinue the drug during pregnancy and when you are lactating. Stomach pain could be explained to a certain degree from the tablet but cannot say that it is totally due to it. So i suggest you to get a urine pregnancy test done at the earliest and to consult with a gynaecologist if it turns out positive. hope this helps and answers your query satisfactorily. Wish you good health, take care.