blood tests for very restricted diet and 12yr old...what am I asking for specifically, beyond the basic fbc thats been done?

[whatthewhatthebleep]

I was a bit surprised in a way that once I'd cajoled the GP to actually take a blood test, that it came back as absolutely fine apparently, apart from some discrepancy with his liver...this is being reasoned away as something to do with the Concerta he was taking for 5.5 yrs? I will be asking for a repeat to be done in a couple of months to see that his liver is ok.

So, I'm surprised really that this has been clear and normal as DS never eats any fruit, vegs (beyond occasional carrots and potatoes), eats fish fingers/fillets in breadcrumbs and chicken in breadcrumbs mostly and my steak pie and ton of puff pastry. Doesn't eat sweets, has occasional chocolate and has copious amounts of milk daily, sometimes with choc milkshake powder in it.

I'm not convinced that he doesn't have any discrepancies as a result of his poor diet and wonder that I should be asking about specific screenings to be done. My DS often gets very grumpy, tired/sleepy, irritable and says he needs to eat something to feel better...I often wonder that he is recognising he is deficient and then seeking something to help him iykwim...he isn't really very good at feeling/recognising when he is hungry or full up so I wonder that it is something else? That because he is so difficult to feed...I find it quite worrying but the fbc says he's fine...does the basic blood test really tell enough about this?

Any advice or what I should ask for?