Change in bowl habits.

I have been expercieng a change in my bowl habits latley. I used to go every day and now I only go twice a week. and it seem every time I go i dont get everything out. I also experience constapation. also i have experinced sudden bouts of nausea and I have nausea when i am using the. should i be worryed im only 18 years old. sorry for the miss-spellings.