Probiotics are good for digestions, if it helps it might be an internal problem. You're on antibiotics - have you considered a fungal thing? Or maybe antibiotic resistance
I have many many many blackheads and closed pores, some of them I extract yield a small yellow sand grain which I think might be keratin, others are normal blackheads, others have stringy white stuff. I started using a salicylic acid wash 2x a day and they are going down, but not gone yet. Salicylic acid is known to be good for lots of clogged pores, you could try that if you haven't yet
I have the same problem! Closed comedones and blackheads are the hardest to get rid of sometimes. Salicylic acid works great on closed comedones and so does mandelic acid. Mandelic acid goes deep down into the pore like a bha but also repairs the pore. It's also an aha so it removes the top layer of skin like glycolic acid. Sulfur also helps with those closed comedones. It brings them to the surface or just completely dries them up.
I've been using salicylic acid, mandelic acid, 10%sulfur and 10% bp for my skin. It's slowly working! My skin was really bumpy and I could squeeze my pores all day and get stuff out. It's gotten a lot better.
What I do for day time is;
Wash my face with a gentle SA face wash. Mario Badescu acne treatment face wash works good.
Apply a thin layer of de la Cruz 10% sulfur ointment, let it sit on my face for 10 mins and wash off with warm water.
Apply a SA 3% moisturizer then a light SPF moisturizer.
What I do for night time is;
Wash face with my Mario Badescu face wash
Apply 10% sulfur ointment and wash off after 10 mins
Apply my 5% mandelic acid toner by makeup artist choice. I apply the toner to my entire face.
Apply some Cerave moisturizer.
Then I spot treat red, inflamed really sore pimples with 10% bp.
That's a lot of stuff but, it's working!!