Perhaps do some research before you buy fish ? Escpecially if you are new to the hobby. I would recommend reading as many books about the type of fish you wish to keep, and then setting up a tank appropriate to their needs. I realise it's hard to resist going down to your local store and picking out the coolest looking fish there, but unless you wanna leave behind you a long trail of dead fish, DO YOUR HOMEWORK ! Your problem is undoubtedly caused by water quality, so make sure you fix it up before buying anymore fish.
I have two pictus cats and they are awesome fish to watch, and the behaviour of swimming up into the corners seems to be normal for them, as my brothers pictus does exactly the same.
Here are some basic facts about the fish I got from one of my books :
PH : 6.0 - 6.8
dH : to 12
Temp Range : 22 -25 C
Provide the pitcus with those conditions and adequte space to swim (this fish LOVES to swim fast ! ) and you shoud have no troubles.