When am I safe?

Melissa • 24, beginning to TTC. Trying to have a safe and healthy pregnancy while FAT as FUCK
Okay, this may sound stupid but if I used the Sunday start method and tonight will start my third week is it effective? 
And also, twice I've been away from home and missed my pill so i took two the next night, I missed my pill for 12-17 and took two on 12-18 and i missed it on 12-24 and took two on 12-25. How much does this affect it's effectiveness?