I had protected sex few days before my period and now my period is late. i also struggle with constipation. could that be the reason or not really ?

Late periods: It depends on how old you are or if you have had intercourse within the "danger" period, but yes missed periods for females almost always warrant a pregnancy test. Spotting can also mean hormonal changes which may be natural as you age, or related to a number of other factors, including stress, nutritional variation, anemia, etc. Recommend you visit an MD clinic to be checked out.