Car wont start - 2005 Nissan Sentra

Sorry it took me so long to get back I took my grandson to see Iron man 3 I will look in to that thank you. God bless

Back in February my car was taking a few tries to start, I took it to my mechanic and he said it was my cam sensor. He ordered a new one and it didn't work at all. Got another one which worked for maybe 3 weeks and failed again. Since then he's got one & tried it and it won't start at all and then out of frustration I got one and put it in myself, same thing won't start at all. So he put the old one back in and "rigged it" so it would start. I guess by pushing it a certain way that makes it start. Its back to the same crap again and idk what to think. I think its more than the cam sensor. Here's what it does. Go to start car, once in a blue moon (maybe 3 times a month it starts on first try) turn key it starts, but not a complete start up and then stalls or turns off. If I hit the gas sometimes it'll rev up but then stall. It takes 20 minutrs most days to get it to finally catch and start so I can drive. Sometimes after it starts and I'm still in park the odometer gauge will fluctuate and it sounds like its almost choppy or stuttering and when its like that I know if I put it in drive it will either stall out or it'll let me drive but my car will jerk and won't drive smooth so ill park it and start it up again and its fine.

The cam sensor popped on the code. But after he rigged it the cam sensor didn't pop up on code again.

I don't know exact codes & I'm afraid to ask my mechanic as he gets offended if you try to figure things out on your own. But he does show/tell me what the codes are when he checks. I know the cam sensor code came up at first. The o2 sensor popped up once but he told me not to get a new one just yet, and a code for my gas tank (which I already am aware of & had fixed once about a year ago, it spits gas out when I pump gas and they fixed the valve but it isn't working still so they need to order a nissan part instead of just a part from the local parts store) those are the only codes that have ever popped up.