I'm not sure what the ingredients are of the products you're using, but I have low porosity hair as well and I found that it hates oils because they sit on top of my hair. They don't penetrate. It weighs down my curls and causes some build-up as well between washes, which could leave it feeling greasy. Also, I used a conditioner that is basically an oil-bomb, so it left my hair being overconditioned all the time.
What I would do (and what I'm trying to figure out myself) is check the ingredient lists and particularly focus on oils and protein. My hair used to be voluminous, but is rather limp nowadays because it lacks protein. I have to cut out oils as much as I can and add protein to restore the balance.
Your hair consists of protein and if you have medium texture hair, it should be able to handle some protein.
I'm not an expert on ingredients, but if you copy them I'm happy to have a look