help?!

So I had my so called "period" but ever since I started birth control it's been very light. Like to the point where I don't need anything but a liner. I get them for like 3-4 days but sometimes they're heavier. This morning I wasn't feeling too great. I felt a little nauseous but didn't really think anything of it but after I ate breakfast it got worse and worse I eventually threw up. After throwing up I feel better but at this point I can't even hold down water. My parents think I might be pregnant, but i don't know. I went and bought a pregnancy test but the first time I didn't pee wnough and I haven't had to pee since. Any advise?