"Healthy" diet is the key; I hear the word "Diet" and think unsustainable weight loss. You need to find a nutrition plan designed that matches body type, sex, and even blood type.
1. Keep a log of all food and exercise for the current routine for 1 week. And continue to keep this, you have to track everything and count all calories in and out in the beginning, don't worry it becomes natural after while.
2. Meet with nutritionist (possibly covered by healthcare insurance or student health centers) and find regular easy to prepare foods that are your staple or base of food. I eat turkey, chicken, yogurt (plain no added sugar but add fresh or frozen fruit), and milk (skim or 1%). All easy to make and can be pretty tasty. This may be the hardest part, but finding healthy foods you also like will help greatly, so search the grocery store high and low. Also this is tough.... give up booze for at least 6 weeks (it works but real hard). Remember all excess carbs get converted into fat for storage and you need to get to recommended daily amounts. Don't cut out all fat, just keep focused on the "good" fats in fish and nuts.
3. Set up a routine for working out, but do different exercises each time.
e.g. write down 21 different 15min exercises (stair master, pushes up, lunges, crunches, etc) and do a different group of 3-4 everyday so you never do the same workout twice. Workout plans like p90x do this for you, but with a little research you can do this yourself. I like p90x a lot, but most women will want to do the "lean" version.
4. Use a heart rate monitor to stay in the target zone when doing cardio.
5. Mix in yoga, helps with strength, flexibility, burns calories, and I think it greatly helps with mental health.
6. Take a multivitamin! I know this seems to be my mission in life, but if working out a lot you simply need a multivitamin. It is hard to impossible to get all the vitamins and minerals you need form food (should say its impossible unless you love vegetables). And most are not designed for athletes or people that work out a lot. Google "Riptrition", it is one of the best on the market now. This will help with mood, decrease colds, and provided greater energy. I personally don't endorse the "fat burners" (that enhance metabolism) although I know people that have had ok results. Definitely stay away from diet pills, basically are speed. Short cuts only set you back in the long term.
Finally, good luck, nothing worth having in life comes easy. Set up a 3 or 6 month goal and stay the course as it take time to do it the right way.