Definitely also trying to gain weight.
5'4" and on SAD I was 110 on average. After starting primal, what body fat I had has melted off and I'm trying to add some of it back on. I think eventually my body will get to some sort of stasis point--I'm still just two months in or so and I can tell my hormones are still doing a lot of recalibrating. My metabolism hasn't slowed at all and living in a city I do a lot of running around.
What kind of weight are you trying to gain? Muscle on primal is easy, I find (not true before for me). Fat is trickier. Seems like you're keeping your food levels up.
I try to aim for 100-150g of carbohydrates every day, and try to make sure my calorie count isn't low, but I find it hard to get to that carb level regularly without somehow incorporating a "cheat" food. I hate tracking my food but I've been doing it and it showed me I unintentionally didn't eat much here and there. Just yesterday, I plugged in everything I ate and I was only at 1400 calories and carbs at 90--this after bacon for breakfast, snacks including fruit and chocolate, lunch with pan-fried liver, more veggie snacks with fat mixed in, a dinner with beef & veggies and a little white rice, and wine. So I made some eggs and had some coconut milk before bed. Have you added up what you just listed? It may not amount to that many calories ultimately, even though it may feel satisfying and you're including good fat.
Other than that, I'm just going with it. I think I need more fat but I don't feel exhausted or undernourished at all, so I'm kind of going to ride it out for a bit to see if my hormones stabilize. I'd really like to be able to just eat when I'm hungry rather than typing foods into myfitnesspal and correcting at the end of the day (I have it set to gain weight). If this keeps up, I'll have to resign myself to the fact that white rice and sweet potatoes will be staples for me. Not a big deal--I like sweet potatoes--but rice tastes like glue to me right now for some reason, even though it goes down fine.
It seems like you're eating enough, but if you're not sure, I'd track it, especially due to the demand of nursing. Also, the fact that you're nursing is surely affecting your hormones and that may be messing with your body composition.
On top of that, since you don't seem to have extra fat stores at the moment, all those extra calories you're eating may be going towards nursing. You may not be able to gain a lot until you're finished nursing. Just some thoughts. If you're feeling undernourished you could see a doctor.
Feel free to PM me if you want to talk in greater detail about this stuff...but yeah, there are definitely women who start eating primal and lose too much weight in the beginning.