I take a lot of fiber (fruit, seeds, flaxseed, chia), drink water, take probiotics and I still struggle with constipation. How else can I help myself?

When you are. Taking in that much fiber (flax, chia seed ; produce) you have to take in a lot of water or it will cause constipation.
Magnesium and Thyroi. Try magnesium, from a health food store. Magnesium oxide, citrate, or a chelated form. Start with 400 mg or so, and progressively increase the dose. You cannot od on magnesium. Too much will cause diarrhea. Take just enough to stay "regular." also, constipation is often one of the many signs of hypothyroidism. Find a thyroid-knowledgeable doctor, who will find a dose that's right for you.