Some dietary help???? Please help!?

Lately I have been missing my period, Idk if I'm actually pregnant or not. Also I have been gaining weight and haven't been able to keep it off. My main concern is the problem I have going to the bathroom (#2). I have done some research and my problem with this has some to do with missing periods and gaining weight. So far I haven't gone to the restroom since friday, and on that day I barely was able to go. It is now 12AM on thursday and I took an enima 5 hours ago and all that came out was a lot of yellowish cotton like things and nothing else. Whenever I do go to the bathroom it's always small and in little . I know this is gross to talk about but I'm really worried. I'm only 18 years old and I don't know what to do about this. Is there any diet schedule I can go with to help me lose weight AND give me lots of fiber?? And what should I do with my problem? My dad won't take me to the hospital unless it's reallly serious.