How can I help a friend who is constantly "ill?"?

I have a good friend and roommate that I am concerned for. She is, like me, in her mid twenties, and is CONSTANTLY claiming she is Ill. I’ve known her a little over a year, and I’m now convinced she may just be a hypochondriac or may have munchausen’s (sp?) syndrome. Now I’m not very familiar with either of these diseases, so I may be totally incorrect- feel free to correct me if I am.

Here’s the deal: since the very beginning she has always expressed how she is concerned for her health. She told me right off the bat how she used to be quite over weight, and lost 100 lbs a few years back. She tells me how she still has an unhealthy relationship with food and is struggling with loosing the extra weight. She constantly thinks about food. She is concerned about her vitamin levels always being low, but she won’t take supplements, and doesn’t eat vitamin rich foods. She says she’s anemic, but I’ve seen the blood work from the last two times she went to the ER, and everything was normal. She’s constantly “feeling faint” weak, and tired/sleepy. She sleeps a good 7 hours at night and takes a 3 hour nap after work.

Basically what I am most concerned about is that she doesn’t see doctor regularly. If she ever feels bad enough she just goes to the ER, but won’t follow up with a doctor afterwards.

I guess what I’m asking is how I can talk with her and help her? She told me before she would like my assistance in eating healthy and encouraging her to take vitamins, work out, do yoga with me,etc… But she’ll always have some excuse for me.
If someone was so sick, why wouldn’t they see a regular doctor? And also, I’m rather sick of always hearing about her health problems… I can’t go a day without hearing how she is sick again.