You might want to step away from the scale and pick up the measuring tape. Keep a weekly log of your waist/hip/thigh/bicep/wrist/etc. measurements. It may also be hopeful to keep a picture log. At the end of the day weight is weight but it doesn't necessarily reflect fitness level. :)

I think the scale is complete BS! Since starting paleo and lifting, I have lost ZERO pounds. None. Zilch. Goose egg. But my stomach is flatter, my "bra roll" is shrinking, and I'm starting to fit into pants I haven't worn in a long time. Put the scale away and grab a camera. Take pictures of yourself and track your progress by how you look, not the scale nonsense.

End rant

I don't think a woman can gain 11 pounds of pure muscle in less than a month, having only worked out a few times. I think it's probably a combination of WATER weight (are you pre-menstrual?), fat and muscle. Are you constipated? Had you already eaten a day's worth of meals? That can add a few pounds too. (If you're gonna weigh yourself, do it first thing in the morning, and always use the same scale.) But agree it's best to not get fixed on a number on a scale and focus on how you feel and look - I certainly can distinguish muscle gain vs. fat gain. Are your waistbands tighter, do you look better or worse in your clothes?

And maybe you should enter a day's worth of food into something like chron-o-meter or FitDay to give yourself a sense of how much you're eating - it may be that you're overshooting the mark a bit.

It could be muscle if you were undernourished before. Really though it's hard to say. I'd be almost certain that you haven't gained 11 pounds of muscle or fat in a month. Is this 11 pounds gain just since starting paleo? What were you eating before? Did you take any other measurements? Have you noticed clothes fitting differently?

If you were on another 'diet' before then it may take a little bit of time for the body to sort itself out, or maybe the weight is already dropping but it went up higher than you realised. There's plenty of information from questions about people not getting the progress that might suggest areas where you could improve your approach, but you really need more information to know if it actually needs fixing or not.

Weight training only 3 times a week, in my opinion, is the PREFERRED method for building mass faster.

Remember, lifting the weights does not cause muscle growth - it's the healing process AFTER lifting the weights that causes muscle growth. I find most weight trainers lose mass if they train 4-5 days a week without proper rest... exception being professional athletes that get certain perks such as monitored nutrition, daily naps, massage/sauna, and "special enhancement".

That being said, I agree with Renee - with the exception of "enhanced supplement users", it's very, very difficult for even a man to gain 11lbs of muscle in a month. But, if you are eating a higher-carb paleo, approaching a pre-menstrual cycle, there is a good chance that you are holding onto some additional water.

My suggestion? Get some tailor's tape (measuring tape) and measure your "trouble areas" (waist, hips, thighs for most). Take a bathing suit/undergarment picture of yourself and print it, writing down these measurements. Do it again in two weeks... and continue to do it until you reach a body (not a number) that you are happy with.

If you are coming off of a year of a controlled starvation diet the pendulum could swing the other way before evening out. No fear though, it'll most likely start moving the right way once you are re-nourished.

If you were having to stay on a tightly controlled diet to not gain weight it would be worth getting a hormone panel done at your next checkup. If you are having endocrine issues those can balance out over time on paleo, but occasionally they don't and require more professional intervention. Time and testing will tell.

I agree with the other posters here, I've had my weight stay static, but my pants start to fit more loosely in the waistband. The scale is just going to tell you your relative likelihood of being blown away in a strong breeze.