Here's an analysis of your supplement stack based on research:

1. Collagen (10g):
   Collagen supplementation can improve skin hydration, elasticity, and reduce wrinkles¹. It's also effective in increasing bone strength and joint health².

2. Creatine (5g):
   Creatine is one of the most researched supplements for enhancing strength, lean muscle mass, and workout performance³. It shows benefits mainly in short-duration, high-intensity exercises and is generally safe within recommended dosages⁴.

3. Glutamine (5g):
   Glutamine is beneficial in maintaining intestinal barrier function and may help improve gut health⁵. While it's popular for muscle recovery, research on its effects in healthy athletes is mixed.

4. Leucine (1.8g):
   Leucine is a key amino acid for muscle protein synthesis, helping with muscle repair and growth. It's often highlighted for its role in triggering this process, but specific benefits depend on overall protein intake.

5. Ashwagandha (200mg):
   This herb has shown potential in reducing anxiety and stress levels, improving mood⁶. Further high-quality studies are required to fully substantiate these effects.

6. Theanine (200mg):
   Theanine is known for promoting relaxation and reducing stress without sedative effects⁷. It's also considered safe for short-term use.

7. Magnesium (200mg):
   Magnesium supports muscle and nerve functions, reduces inflammation, and may alleviate muscle soreness⁸. It's beneficial if your dietary intake is insufficient.

8. Vitamin D3 (400 IU):
   Vitamin D helps maintain bone health by aiding calcium absorption⁹. Pairing it with Vitamin K2 may support bone density, but if your diet is rich in K2, supplementation might not be necessary.

9. Iron (7g):
   Typically, iron supplements are useful in addressing or preventing anemia by aiding red blood cell production¹⁰. However, 7g seems like an unusually high dose. It's crucial to monitor and adjust under medical guidance.

10. Zinc (7g):
    Zinc is involved in numerous biological functions, including immune function and protein synthesis¹¹. However, similarly, 7g is far above usual dosages and should be reassessed.

11. Calcium (250mg):
    Calcium is crucial for maintaining strong bones and teeth¹². Ensure your overall intake (diet plus supplements) meets recommended levels without excessive amounts.

12. Berberine (500mg with high-carb meals):
    Berberine may help with blood sugar regulation and has been explored for improving lipid profiles¹³. It's still advised to consider its interaction with other medications.

13. Melatonin (3mg for poor sleep):
    Melatonin can support sleep cycle regulation and reduce the time to fall asleep¹⁴. It's generally considered safe for short-term use.

Regarding multivitamins, they can help fill nutritional gaps, but their necessity depends on your diet's adequacy¹⁵. It's always a good idea to review your overall dietary intake and lifestyle needs to decide on supplementation.

Ensure to consult with a healthcare professional for tailored advice, especially about high-dose supplementation like iron and zinc.