Doing the Normal everyday stuff and the charger came with the box is what I'm using
I think the question was really what are you doing when it is charging (though your "normal everyday stuff" and mine might be completely different, so it's one of those answers that doesn't tell us very much

). So if you are gaming while charging then this may be normal (indeed the phone might slow charging to protect the battery if you are doing that - or throttle the processor!).
But if you are using the supplied charger and cable and it's not charging then unless you are using it heavily, or it is very hot or cold where you are, then something is wrong. Personally I'd be tempted to try another cable, or if you haven't got another USB-C-to-C lead try your old charger with a USB-A-to-C lead (useful to have one of these anyway, unless your computer only has USB-C ports too). A defective cable can result in extremely slow charging, so if you just got a bad cable that might be all there is to it.
If you try a different charger and that works then you'll know that your problem is either the charger or the cable, but not which. In that case cable is easiest, but you could see if they'll replace it. If a different cable and different charger make no difference then it's something with the phone.
You won't get fast charging from an old charger and an A-to-C cable but that doesn't matter for this purpose: if it charges normally that will tell us the phone is ok (and my Pixel 2 charges pretty quickly using chargers that don't support USB-PD. Actually it charges as fast from my laptop's USB-A port as my previous phone charged from its charger).