unfortunately the only easy reliable cheap method i can use is abstinence.
stupid body.
You do have other options, but there are risk/benefit tradeoffs. Despite its high failure rate, there are many people who use the rhythm method (see for example
http://www.epigee.org/guide/rhythm.html). I know several people who have used it with no failures (as has my wife). When we wanted to get pregnant, it was the usual plus rhythm method in reverse (plus added basal temp for greater accuracy). It does have a high failure rate and is completely inappropriate for your typical premed or med student. To be able to use this method successfully, it really helps if the woman has a very regular cycle, and even then the woman needs to have a very good handle on what is going on throughout her cycle, using various ovulation checks such as basal temp and ovulation testers to establish a very clear idea of the usual pattern and common variations that come about with stress and illness. After a while you might be able to tell when she's getting close to ovulation from signs like the viscosity & stringiness of the vaginal mucus alone (but I wouldn't start with that until you have several years of experience). Of course, the only people I know who use this method are married, a situation in which you're not (hopefully) especially worried about STD's, and, if she does get pregnant it was something the couple was prepared to deal with even if it wasn't the current plan.
The rhythm method is a complicated, low reliability method compared to just taking a pill, patch or using an IUD, but if you can't tolerate the hormonal methods, don't like condoms, are irritated by spermicides, don't want an IUD in the uterus, don't want to bother with a cervical cap, you start to run out of other options.
Here is a good site for information on the various methods:
http://contraceptiononline.org/patient-handouts/
Side effects for the Mirena IUD are ...
"Changes in menstrual bleeding patterns are the most common side effects of the IUS. During the first 3 to 6 months of use, the number of days of bleeding and spotting increases and bleeding patterns become irregular.
... Other side effects include lower abdominal pain or cramping, reported by about 10% of users during the first 3 months. Side effects occurring in fewer than 5% of women include acne or other skin problems, back pain, breast tenderness, headache, mood changes, and nausea.
Copper ... "Some women who use the IUD have more bleeding during and between their periods. The copper IUD also can cause cramps which can be helped by an over-the-counter pain medicine like ibuprofen or naproxen. The cramps can go away after the first few months as the uterus gets used to the IUD."
