Uh-oh, gaining weight?

For the last few weeks, I've been eating healthy (no sugars, no simple carbohydrates, balanced diet) with an average of 1200 and under calories a day. 4 days a week, I've been going to kickboxing for 2 very intense hours, and on off-days, been going for walks and/or jogs. I've been toning down, my pants and shirts are getting to big for me and i'm seeing muscle definition...and I went down to 149. This morning i woke up, and weighed myself. 152.5!!! What happened?! I haven't increased m;y eating, have decreased my exercise....is it possible i gained this weight because my time of month is coming soon, or is there another reason? HELP!