What Causes Delay In Menstruation?

good day iam a 25 year old lady and usually get my periods at the beginning of a month if not then at the end i havent had my periods in a month and a half now but have taken two pregnancy test witch wasnt during the morning and both were negative. i am experiencing discomfort when i sleep my nipples are sore i get cravings sometimes but nothing weird and now and again i feel nauseas my tummy also feels like its bloating up could i be pregnant?