Why do I feel nauseated all the time?

It's usually right after I eat. I never vomit, I just feel really queasy, sort of a similar feeling to car sickness or motion sickness. Maybe 4 months ago, I had heartburn ALL THE TIME it seemed. I started taking OTC heartburn stuff on occasion; I don't get heartburn anymore, but now I always feel nauseated. It doesn't matter what I eat; I can eat heavy food or light food and I feel the same. I just just as sick after having a cheeseburger as I do after a salad with no dressing or a cup of fresh fruit. Help! -- Some background info on me: I am a 24 yr old female; I am on Ortho Tri Cyclen (have been for almost a year); I am very overweight but I have been overweight since childhood and have never had any health issues besides asthma onset by a severe case of bronchitis when I was very young; I take my Ortho religiously, never miss a pill and am rarely late, so although I have regular with my boyfriend, I highly doubt there is even a chance I am pregnant (had my last period 2 weeks ago); I have been taking OTC ranitidine when I start to feel nauseated, but it is not helping much (helped with heartburn, though).