It's one of my fears LOL. Every time I'm late I start getting a bit antsy and even 2 months ago I was nudging 60 days on my cycle and I did do a test. It is entirely possible to fall pg again afterwards and some techniques do have higher chances of failure than others - usually the one where they use clips on the vans deferens instead of actually cutting and suturing them. Maybe it's just one of those things - I notice as I'm getting older my cycle is changing a lot too now as I head towards peri-menopause but it would probably put your mind at ease if you did a test.