A couple of thoughts... (ps I am a P90x graduate myself)
You shouldn't be sore all the time if you started in January. It can be a sign that you are stressing your body too much. The first few weeks yes, when starting a new program, but being sore is not an indication of muscle growth.
P90X, assuming you are putting in full effort (and I suspect maybe too much effort if you are always sore), will make you very very hungry - it is practically cardio because it is meant to be done with light weight/high rep (12-15). You would be burning a lot of calories. Are you following the nutrition program?
P90X itself is unlikely to produce 5lbs of muscle gain in a female in 2 months, even very heavy lifting (ie. a 150lb squat) would make that difficult due to hormones.
It's likely a combination of:
Recomposition (some muscle gain, but not 5lbs, with some fat loss)
Water retention (if you are pushing too hard and "always sore" then you are likely retaining a lot of water as well on a frequent basis)
Possibly eating too much food due to the amount of exercise you are doing.
BUT
"You love the results" ~ then please, TOSS THE SCALE! If you are loving what you see in the mirror, who cares what the # is !!!