I went to the dermatologist finally and he studied my scalp. He said that most likely the thinning was caused by a stressful event from a project I underwent 3 months prior to the start of the thinning. This can happen and is called telogen effluvium. For whatever reason the cowashing may have been exacerbating the shedding, which decreased radically after I stopped cowashing.
Bottom line is if you think your hair is shedding excessively or thinning, you should get yourself to the derm ASAP. If you think you're getting a negative reaction from anything you're doing or using, stop right away and consult your derm and/or your family doctor.
Below is a link to the thread I posted in General Discussion. I wanted to give you a heads up here in case you were starting to cowash and missed it. I'd appreciate it if you left comments on the original thread, so we don't have too many threads on the same thing.
Please please if you're starting to cowash keep an eye out on the density of your hair. Measure your ponytail before you start and keep measuring weekly. If the density decreases, please stop cowashing. I didn't really keep an eye out on the density and when I finally figured out the flatness of my hair wasn't only from styling and products but also from my hair THINNING, I had already lost a pretty good amount of hair. It's very noticeable now and I'm very sad about it. I wish I would have stopped earlier.
Please be careful. Though I realize this doesn't happen to everyone, it happened to me. If you search for "thinning, thin, cowashing" or other combinations you'll see other threads from other curlies experiencing the same thing. Please learn from my mistake.
Based on my experience I couldn't recommend co-washing. (Low-poos on the other hand have given me no problem). If you proceed to cowash, please proceed with caution. Take good care of your hair.