Im feeling sad alot, help!?

ok so for a few months, i have gone over to my freinds house everyweekend. its really fun there and i love it. i also have baseball, and weight training after school some days during the week. the only time im usually at home is nights before a game, and school nights. alot of school nights are cut short because of practice and weight training, so i have not been at home alot. also, i have been an only child with a single parent for 14 years, and now my mom is getting married to someone, and i will have a stepbrother. there is little time where i am at home and especially at home alone with my mom. it was all fine, and then it seems like overnight i all of a sudden really missed being at home with my mom. i went to school and left early sick because i was so sad. now i am just feeling sad alot. i have to go to school tomorrow, i dont know what i am going to do. i really miss my mom now too even if we are away for just a few hours.