Cramps...could I still be pregnant?

My last period was on Dec. 19, 2006. I ovulated on Jan. 6th and my husband and I tried to get pregnant. This past weekend I started feeling cramps (similar to the ones I get a week before my period). The cramps have lasted about 5 days and are still going strong. Could these be implantation cramps or are they regular period cramps. I'm not due until the 20th of Jan.
If they are regular period cramps, why do I get them a week before my period starts? Is there something wrong with me?