Hi Rubes.
I am no expert but it sounds like it could be split ends. Excessive brushing of hair when wet will cause them and excessive straightening will cause broken ends. This can make your hair tangly. Most hairdressers are horrified by using a brush on wet hair.
Just get your hairdresser to remove any split ends for you and try using a comb on your hair when it's wet. A detangling comb is best as the teeth are smoother and further apart. Always comb the conditioner through your hair before you rinse it out too. I picked that up from some celeb hairdresser or other years ago and It does make a difference I have found.
Even if your hair is long and without any layers you should get the ends trimmed off every three or four months too.
When your hair feels tangled, start by detangling the very ends of your hair first and work your way up the hair, combing downwards of course, as the tangles below are removed. This helps to minimise causing more split ends.
Your hair could be a little dry from over washing it too. The natural oils are not getting a chance to distribute through your hair and serum doesn't really compensate for this. It isn't the same and it is thicker and heavier. It could actually be the serum that makes you feel the need to wash your hair every day.
Try only washing your hair every other day. You should really get it down to washing it just two or three times a week to keep it in optimum condition.
These tips have always worked for me and I am often complimented by my haidresser and my friends on the condition of my hair. I hope they are also of help to you hon.