Sounds like breakage to me.

if you get a trim, and your hair feels thicker.. then as time goes on it thins out again thats breakage & you need to take better care of the ends.
Protein is important to stop breakage but you must also make sure the ends are moisturized because them being dry and brittle will also lead to breakage.
My hair used to be like that, now I do regular protein treatments and I always add extra sealant or moisturizer to my ends
dense, fine & porous curls |

Poo/Cowash| Bobeam, V05 Shea Cashmere
DC| AOGPB, CJ Repair Me, BrownButterBeauty
RinseOut| Mill Creek Keratin Conditioner, Ology Moisturizing Conditioner
Leave In| Curl Rehab, Bee Mine Luscious Balanced Moisturizer, CJ Smoothing Lotion
Moisturize|Oyin Hair Dew, CR Moisture Milk
Gel| Kiss My Face UMG, Trader Joes Aloe Vera, KCCC
Sealants| Aloe Juice, Whipped Shea, Cocoa & Mango Butters, Castor, & my Peanut Oil Blend =)