Ads Disappearing Once Site is Loaded

My website is healthymomsmagazine.net I am a publisher for Sovrn/Lijit and have installed their ad tags on my site following their instructions. When my site is loaded the ads appear for about 5 seconds and then they disappear. Sometimes they don’t appear at all and they are showing blank space instead of the ads. I’ve searched the forums, asked for help from Sovrn, asked for help with the developers of my theme (Zoom), but nobody knows how to fix this. Please, please help!