I think I have a tapeworm?

For like 4 months now, I've been EXTREMELY nauseous, having widespread pains in my abdomen, low appetite or none at all and losing MAJOR weight. I am 5'10 and I've been no more/no less than 152 lbs. Now I am 119 lbs without having exercise. Everytime I eat, I get sick! I haven't vomited but sure fell like I was going to. The doctor diagnosed with GERD at first but the medicine (Nexium) wasn't working. They also put me on a Carnation Instant Breakfast/protein diet so I could gain weight. My weight STILL decreased. This took place two weeks ago when I was 122 lbs. Today, I had to get a depo shot, which I don't think was a good idea but yeahhh. I have a referral to the GI doctor on Tuesday which they should've done a LONG time ago. Any ideas? I really need some guidance.