You need to closely monitor your caloric intake. I did this when I had irregular periods and I was shocked at how low it was (I used cronometer). If it's low you will need to start forcing yourself to eat more calories, either by eating more food or by adding more fat to your food or both (haiga rice or yams with ghee for example). You are going to have to adjust Cronometer for the amount of exercise you are doing and your goal weight (which should be higher). You'd be surprised at how many calories you need and how hard it can be to get them on paleo. Based on my Cronometer, it says for your height and weight with high activity and a goal of 120 lbs, you need 2700 calories a day. Your weight is way too low right now so I suspect this is an issue. I was have issues at 5'2" and 100 lbs and you are significantly taller. I'm now more around 110.
Most of the weight gain has been concentrated on my backside, which is exactly where fat in women is supposed to be to maximize fertility. Some people will tell you that you can't spot gain or reduce, but these fat masses are hormonally regulated and altered your hormones can alter their size. I would also recommend eating roe, grass-fed ghee/butter oil, and cod liver oil. I've had other women tell me that they've gotten good curves and better cycles this way.