hiii
well dude the problem is not with u .. the problem is with FIITJEE ppl .. it always a case with them ... i have experienced .. they make the paper so tuff for some papers that it is impossible to solve them .. It must be happening with other students also .. just check it out ..
Moreover .. is it that u score well in the first paper of the day ?? Is there somehting like that .. if yes then dude try to concentrate more .. u need more energy .. rite ..
Do question frm ur own book and see if u can do them .. in all the three subjects .. or one more thing that u can do is to try out the paper of some previous years JEE .. u will come to know wat is happening ... okay
Now about the OC book .. well i wud prefer the Arihant book .. rest u can choose .. okay
cheers