I mean, you'll see gains, but to really pour them on you need to eat a calorie surplus and take in a lot of protein.
Cant emphasise this enough bruv,
OP you need to really EAT like its going out of fashion.
3 X a week is a decent frequency but just try and ensure this PT brederin of yours ain't taking you for a twat, making you do stupid meaningless shyte whilst he milks your wallet.
Jump on a PROVEN strength training regime (ask your PT about - SL, 5X5, Madcow, Wendlers, WSFSB) to develop functional strength/CNS & a solid foundation.
Seeing as you're at the Noob phase, them gains will come rapidly first 6-12 months. You should start filling out nicely if you eating and lifting right.
Goodluck & yea what
@GinaThatAintNoDamnPuppy! said welcome to the dark side......The IRON obsession is REAL....better that addiction than cultivating a trendy drug habit