HELP: Food addiction + unhealthy lifestyle

So I've struggled with an unhealthy lifestyle from childhood but I'm officially embarrassed and need to lose the weight. I'm almost 21, 5'8, weigh about 300 lbs, and I have PCOS. I have a 1 year old son that's getting more and more difficult to care for and we're wanting a 2nd baby in the near future as well, which would simply be irresponsible of me given how my weight complicated my last pregnancy when I had started at 265 lbs.

I'm throwing out the unhealthy food in my apartment and getting a gym membership at the end of the week as this has had some success for me before but I've never been able to lose more than 20 lbs in the past so I'd like to hear some advice from anyone who's been in a similar boat as me and had success losing 50-100+ lbs.