p90x gaining weight

So I know I've read posts on here about gaining weight at the start of P90X, but I'm still a little concerned.

First, a little background info. I've started weight loss efforts multiple times in my adult life. Due to my size, it is not unusual for me to lose 15 or so pounds in the first couple of weeks.

All that said, I started P90X last Monday (Oct. 22). I did the first four days (substituting cardio x for plyos and yoga x - they both gave me severe headaches). After those four days, schedule got in the way (I still did activity on Sunday, but it wasn't P90X). Since I didn't stick with the full week, I decided to restart from Day 1 this past Monday (10/29).

I "unofficially" weigh myself almost daily (officially only once per week), and have been gaining weight almost every day. Is this something I should brush off, or am I doing something wrong? If this is typical, how long can I expect the weight gain to last?

I should point out that my goal is to lose weight (when all is said and done, hopefully between 80 and 100 pounds). I know that muscle work and cardio combined are a powerful plan, hence the P90X.

TL;DR - I'm fat and need to lose weight. Been doing P90X for about a week and a half and have gained weight almost every day.