im new here! but downstream o2 sensor is giving me a hell of a headache!

:D

my car is acting up....

When I first start it shakes like crazy for about 1 minute and if you heat gas nothing will happen it wont go... it eventually goes but very slow...
01 sentra with sr20

it does this shaking thing also on the expressway... no matter at what speed it just loses all power and it shakes...

I thought it was the o2 sensor and i tried to replace it but the damm thing wont come out... i used every tool i can think of till i chipped off the bolt head and now it wont come off...

so basically.... i have the following problems:

1. car feels like i have no power...
2. o2 sensor is impossible to remove...
3. i am pissed off


please help any suggestions are welcome

I drive a 01 sentra sr20 like yours! Have u replaced ur spark plugs,wires, rotor button and cap?