Hi Jennifer, Im not sure how good with the advice I can be, however, my LO, was diagnosed with Lactose Intolerance at 3 months too. He was prescribed LF baby formula until he was about 15 months.
I Tried then to start using normal cows milk but he was like your LO and became quite bloated and constipated or had nasty diahorrea within days of trying.
I have managed to find a lactose free semi-skimmed milk called 'Lactolite' which is normally with the cartoned milk in the supermarkets here in the UK, not with the fresh milk.
It has been a real success, its something like 95% LF so he seems to be fine on it and he's now 28months old.
I hope you can find something that your LO can have as a replacement or your LO may be ok with the normal Cows milk, you could try with little amounts at first and see how it goes.
I know its worrying, I was the same. Hope it goes ok for you