“Thinning hair?”

I have noticed that my hair feels thinner. I usually have thicker hair and I can usually feel it weighing down on my head. I wonder if I experienced some hair loss and wonder if it is something more serious. I noticed this three days ago when I washed my hair and was using a different shampoo and conditioner. I didn't feel any clumps coming out and see no bald patches. Since it was a different shampoo and conditioner, I really had to scrub it out and maybe it scrubbed too hard and for too long. I also brushed it while it was very wet and tangled. There was a medium clump of hair in the drain when I checked but my father said that he hadn't cleaned the drain in a while and this was most likely built up from weeks. My hair is still thick, but I feel like it could be thicker. I have hypothyroidism (have for a while now) and take medication for it and I also smoke, but I have never experienced anything like this before. Lately, I have also been wearing it up in tight ponytails and buns. Now, I still see some shedding on my pillow or in the shower which I know is normal. The hair sometimes has a white bulb on the end of it and I want to know if that means something serious. I can normally see a little bit of my scalp with my part and if I move the hair on the back of my head a certain way. I have experienced some itching since that last shower. I want to know if this could be something serious.