[US] issues with melatonin

I have a 3 year old who has been experiencing or struggling with food aversion for about two years now. When it first started his father and I were separating and there were a lot of issues with the nanny, who ended up being fired , actually the judge told my ex that she had to be fired immediately,

Anyways, I pushed for our child to see a GI doctor and nothing has been found. Our child was sleeping excessively and stopped talking around 1 to 1.5 years old. He was in speech therapy and it worked wonders. Once we were living in our own house his language exploded.

He would come back from visitation with his dad saying his tummy hurts. I tried everything I could to figure out what was bothering him. His food aversion became worse and we started feeding therapy. I thought maybe it was dairy so we went dairy free.

Once his dad was allowed to have overnights, the night terrors started. I thought dad was giving him dairy and not telling me. But I couldn’t ask dad, he would lie.

Any ways long story short we decide to go on a cruise for older brother graduation. Now on this cruise our 3 year old sleeps the entire day almost and still sleeps at night. We have separate bedrooms and the kids are with me so I think we are safe right. Three year old is super irritable the whole time and wants to sleep and go home nonstop. I figure he’s just worn out from the trip or something.

Now I’m unpacking things at my exs house and putting our child’s clothes away. We’ve been pretty amicable and I try to keep the peace. But I find a little container and open it. Inside are some pills. One looks like adderral and the others look like melatonin. I’m not really sure how to get them tested or what to do but I know if I confront my ex it will not be safe.

So a month later I’m sitting here putting two and two together and wondering if my ex has been microdosing melatonin to our toddler all along? Ex has been through medical school but never became a doctor. Not sure why.

The only advice I can find online is to take my child to the pediatrician and tell them his symptoms. But if the melatonin has left his body by the time of our appointment then would it even show up in testing? And then they may call cps and if there is not proof then I just end up looking crazy.

What is the logical solution and what do I do here? From a medical standpoint … how can I actually find out what is going on. Because if the melatonin is causing gastritis and food aversion then we should address it from that standpoint instead of searching aimlessly for answers…

Oh to make matters more difficult for me, the father’s mom is a well respected pediatrician In our small town so I cannot go to just any other doctor with my concerns, as they are all friends…this happened with the GI doctor and he basically acted like I was being crazy or making things up…