Menstrual cycle problem? (Age 23)

My last period ended on Feb 27th and I haven't had a period since then. I took a pregnancy test a couple weeks ago and another one this morning. Both were negative. My periods are always irregular but never to where i don't get a period for two months. Occasionally it will skip a month. But anyways, my question is, when do you think I should contact a dr? The only symptoms I have are occasional cramps which have been going on for a few weeks and a had sore beasts last week. Should I wait another month or do you think there's a problem or pregnancy that should be addressed now?