As people age sensitivities, allergies change. You may now be sensitive to milk. Milk,corn,eggs ,gluten and much more can cause allergy reactions in the gut like constipation, running nose, hives ect..
Maybe you need to do a cleanse to remove impurities like metals , toxins/PCBs to remove the disruptors in your body. If you have disruptions in the body your gut flora won't even work right no matter how much probiotics you take. I'm currently battling this issue and it's gotten so bad it's caused anxiety brain fog ect...