The "Constantly Changing" Law of Locks
This last photo indicates to me that it is indeed overdrying caused by baking soda. You know how I know?
Look at the circled areas on the photo:
Now even if the bottom one is simply the another dot/star showing through from your shirt, the other three are definitely not. I know what those thicker areas are on the hair shaft- breakage waiting to happen. I guarantee that if you go through the tips of your hair you'll find lots of them. If you grab the very tip of the hair with your finger nails and pull it'll snap off right at the thicker dot area.
That's exactly what i had going on until I started using shampoo bars with good moisturizers. There's quite a few soapers who make them. Mosalu on Etsy is one of my personal faves. I've never tried the brand sponsored here on this site but heard very good things about it. Take a look at the ingredients of the dreadlockshampoo bars. Those are the ingredients you need in your dreadlocks! Nothing fake. For the love of all that is holy, do not ever try to use 'glycerin soap' on your locks. It's 'melt and pour.' Cheap. Drying. And really really really bad for your locks. There are more soapers selling those now, though, and it's truly sad. They don't know what they're doing to people's hair. So you gotta read ingredients.
After you've used good shampoo bars for a while you' noticed these areas of your hair getting better. They'll break off, yes, because that's the only thing for them to do once it's gotten that bad, but you wont see a whole lot more of them starting up. Your hair will heal and man oh man will it feel completely different than it does when you're only using baking soda!!!!!!!!!
The one that's staring to 'thin the middle' it looks to me like all the knots are being pushed down to the end of your lock. That can happen sometimes. I've got a few of those myself. But the rest of the lock up to the top is strong so as long as the hair is well taken care of and not dried out anymore you should be fine.
I've never tried it, but I have heard that jojoba oil is most like our skin and hair structure so it is easily absorbed. Taye's idea might be worth checking out. Just bear in mind though that when you put oil on your hair you're going to be more inclined to shampoo that area of your hair with more soap to get suds and be a little more rough with it in general, feeling like you have to get it all off for your hair to be clean. Then you put more oil on after your hair is dry. Then you shampoo it off. Then you put more on. Do you see where I'm going with this? It's a cycle I found myself in not too long before I quit and started locking up. The constant stress was wearing my hair down. But if you're sparing with the oil(UNLIKE I was!) and are mindful when you wash not to be too rough then you will much more than likely have great results.
updated by @angel-frye: 07/22/15 07:42:13AM