Quoting L&B +1:" Ever since Ive had my period Ive known right when I ovulate...now 6 months after having my son I have ... [snip!] ... BC, just using condoms) once after saying ok lets do it...but now that I think about this weight issue I'm 2nd guessing things!"
I ask because when I was 290 (5'5") I wasn't ovulating anymore. It took about a 20lb weight loss for my cycles to become very regular again. I would (at first) work on losing just enough weight to get my cycles back. If they're irregular because of weight, then the weight is causing your hormones to be not compatible with pregnancy. If you do get pregnant, the eggs is more likely to be of lesser quality and you're more at risk for miscarriage because of that, and also more at risk for miscarriage because your hormones are out of whack.
At 290 the prospect of losing weight to have a healthy pregnancy was very scary for me. I failed at every diet I had ever tried and I was terrified of failing again. Having such a small weightloss goal gave me the courage to go for it. My doctor put me on an Atkins diet and in the time it took to lose that little bit of weight I learned a lot about changing my lifestyle instead of dieting, and about choosing foods for satiety and ignoring calories which caused me to consume less calories in the end. I also found a way to work out that was actually fun.
Once I got my cyles got back on track I had begun to feel really empowered by the lifestyle change. It was comfortable for me and I knew I could keep it up long term so I had the courage to continue with it. In the 2-3 years since I've lost about 50 more pounds. It is slow progress. However, it is not the amount of weight I've lost that is important, but that I have been able to keep off every pound I lose.
Good luck with it all. I know it's intimidating! I hope whatever you do the result is a healthy baby and healthy mom.