Probiotics can be beneficial in addressing some of the issues you're experiencing, including gastrointestinal symptoms and skin conditions related to the gut-skin axis. Here's how probiotics may be relevant to your situation:

1. Gastroesophageal Reflux Disease (GERD) and Digestion: Probiotics have shown potential benefits in alleviating symptoms of GERD, such as regurgitation, heartburn, and associated upper gastrointestinal symptoms like nausea and abdominal pain¹². This could help improve your acid reflux and digestion issues.

2. Skin Conditions and the Gut-Skin Axis: Probiotics might play a role in skin health through the gut-skin axis. They can help regulate immune responses, reduce inflammation, and may aid in managing skin conditions like rosacea and seborrheic dermatitis³. This effect is due to the ability of probiotics to maintain intestinal microbiota homeostasis, which can have downstream effects on the skin.

3. Sinus Congestion and Allergies: Although the direct impact of probiotics on sinus and allergy relief is less researched, maintaining a healthy gut microbiome might contribute to overall immune health, which can indirectly impact allergic reactions.

Regarding your concerns about potential Candida overgrowth, symptoms like a persistent white tongue can sometimes indicate an imbalance in the oral or gut flora. Probiotics might help in restoring a healthy balance, but if you suspect an overgrowth, consulting a healthcare provider for diagnostic testing would be wise.

Additionally, considering allergy sublingual drops while using probiotics to heal the gut can be a viable option, as these drops target different mechanisms. However, it would be best to discuss this combination with your healthcare provider to tailor it to your specific needs and ensure it doesn't cause unwanted interactions.

It seems you're dealing with a complex interplay of dietary sensitivities, stress, and gut health issues, which might influence your sinus congestion and skin conditions. Here's how tailored use of probiotics and dietary adjustments could help:

1. Histamine Intolerance: Given that you suspect histamine intolerance, it's crucial to choose probiotics that do not produce histamine. Some probiotic strains may exacerbate histamine issues, so opting for strains like Bifidobacterium infantis, Bifidobacterium longum, and Lactobacillus plantarum may be beneficial, as these tend to degrade rather than produce histamine¹.

2. Carbohydrate and Gluten Sensitivity: A lower-carb, higher-protein diet could be supportive if you notice improvement in symptoms when reducing carbs, which sometimes ties into managing insulin spikes or addressing potential gut microbial imbalances. Additionally, reducing gluten might help if you have a sensitivity, as gluten can sometimes exacerbate gut inflammation.

3. Sugar Alcohol Sensitivity: The sweeteners in protein powders that irritate your stomach are often sugar alcohols, like sorbitol or xylitol, which can cause gastrointestinal discomfort. Opting for unsweetened protein powders or those sweetened with natural non-irritating alternatives could help.

4. Fat Digestion: Difficulty digesting fats may indicate an insufficiency in digestive enzymes, particularly lipase. Digestive enzyme supplements, especially those containing lipase, might support fat digestion.

5. Sinus and Skin Connection: Reducing dairy and potentially gluten seems to be a positive step considering your response. Continued observation and elimination can help identify specific triggers.

6. General Recommendations: Monitor your diet closely, keep a food and symptom diary, and consider consulting with a healthcare provider, such as a gastroenterologist or an allergist, for comprehensive testing and advice.

While probiotics could be part of your solution, they are most effective as part of a broader strategy that includes dietary modification and addressing any underlying health issues.