In what form are you taking the praziquantel? Is it the proper 600mg tablets or is this some powder or something that you are taking?
Praziquantel is vile tasting stuff (bitter and whiffs like dung), so if you try and chew it (or take it in powder form) you'll want to vomit. Make sure to swallow tablets whole and wash down with as much water as you can drink. Take a small amount of food after that to make sure it is down and to take that vile vomit-inducing taste from your mouth. Once it is down past your stomach I found praziquantel OK.
I also found a good strategy was to take in big doses at once and not give the critters any warning shots to escape from it. The first big dose was easier to take than lots of smaller doses too (less having to bear the lingering disgusting taste). I don't know your weight, but I am 85 kg and found taking 5x600mg tabs at once easier than several smaller doses with the taste lingering for longer, so maybe easier for you if you increase your initial dose from only 2 tabs.
Also, wait at least 6 hours between doses instead of 4. I vomited once on Praziquantel and it was the only time when I left 4 hours between doses.