I also get cramps a week or so before my period. It always makes me think my period is starting, but then it doesn't. Ugh! When the cramps occur, I take ibuprofen (Motrin) or naproxen sodium (Aleve), and these medications usually make the cramping stop. You can buy the name brands or often find generic substitutes that are cheaper. They are similar chemically to aspirin, so if you can tolerate aspirin, you can probably take them with no problems. I always take them with food, because they can be really hard on an empty stomach.
Sometimes medicine like Midol or Premsin can help. These contain mild diruretics to help reduce swelling and water retention as well. I think they also have a mild antihistamine that acts as a very mild sedative.
If over-the-counter meds don't help your condition, you might see your dr about prescription options or other treatments.