What Causes Constipation, Fluttering In Abdomen And Light Periods?

I am 40 years old. I was only one day late and then had a weird period. Very light at first, but with heavy cramping and then as my period progressed, had more of a moderate flow. It was an unusual period. I'm normally like clockwork and it usually begins very heavy and tapers off by the third day, then comes back with a moderate-light flow. Negative pregnancy test one day before period was due. Now constipated and have weird fluttering (gas?) in upper left abdomen. I'm also occasionally nauseated and didn't drop any weight following the end of my period, as I normally gain 5-8 lbs. Should I take a pregnancy test?