Not certified yet? Are you in an Open Water class? Or just trying to do it all on your own? If you're not in a class, I'd highly recommend you get in one before you really attempt any further. First and foremost from a safety standpoint. But also so you start off learning properly and not creating bad habits from poor technique/lack of training. Is it rocket science? No, of course not. But still something you want to learn to do right from the first time rather than doing it wrong repeatedly and then having to unlearn poorly developed skills. I hope that makes sense.
As for your decent problems....more information is needed. Water type? Wetsuit? Thickness? Body mass? How much lead are you carrying? Aluminum tanks or steel? Not knowing any of that information, I'd assume your issue is one of two things. Either you're not breathing out enough to get yourself that first couple of feet below the surface or you're improperly weighted. And if I had to put money on it I'd say it's likely the latter, which just proves you need to be in an Open Water class.