Hello, having periods twice a month means shorter menstrual cycle of less than 20 days duration. The normal range of menstrual cycle is 21-35days. You are having polymenorrhoea which depending upon your symptoms and other health problems should be treated otherwise you ll become anemic and weak. Meet your gynaecologist and get blood tests for hemoglobin and transvaginal ultrasound and other investigations done as per requirement to rule out the causes of polymenorrhoea. Get proper treatment for the cause and regularise and normalise your menstrual cycle. It is possible to get pregnant with irregular period by maintaining menstrual calender and having sex regularly from 4 days before and 4days after day of ovulation. The day of ovulation can be calculated by substracting 14 from the date of the starting of the next menstrual cycle if you can predict it by maintaining menstrual calender. Having regular intercourse for 16months with unsuccessful results is not normal and the reason of being unsuccessful at conceiving should be found out and treated. Usually pregnancy occurs in 12months of regular unprotected intercourse. Both partners should cooperate. The male partner should have his seminal fluid analysis should be done.