Don't let them tell you it's IBS unless they do tests to rule out things. It's what's called a "diagnosis of exclusion." But too many doctors are lazy and just label people with it without considering other things because the symptoms fit. Ask the doctor what other conditions could cause your symptoms and what tests need to be done to check for them.
IBS and other intestinal conditions can be aggravated by stress, but also by diet. Make sure the doctor gives you information about what foods to avoid and which to eat more of to help your symptoms. I would suggest keeping a food/stress diary. Write down everything you eat, along with your stress level and what symptoms you are experiencing at the time and their severity. Every time you eat something or have a change in symptoms, write it down. This will help you and the doctors find what triggers your issues. For example, if you have problems every time you drink coffee, that could be a trigger. So then you'd avoid coffee for a couple of weeks and see if things change.
Regardless of your intestinal problems, it sounds like you really need to get your stress under control. It's only the first week of university--why are you stressing so much? Figure out what you are afraid of or worried about and ask yourself why. Is it the amount of work? The unfamiliar environment? Being away from home?
Look around and find something extracurricular that you will enjoy, such as an aerobics class, pottery (very therapeutic), painting, basketball, film club, crochet, or whatever you are interested in. Even if it's just once a week. Don't make your life all about school and work. Take time out for you. Ask your boyfriend to do the activity with you.
If you really can't handle the stress, talk to your doctor about it.
Good luck with everything. Write back if you need anything else or if it's just to vent.