Hi OP,
You are not stupid and you CAN do this. Never let a past learning experience make you think that you can’t learn something now.
I’ve been using Duolingo for a couple of years now, to learn Italian. And it sounds like you’re being too hard on yourself with your expectations. First of all, it’s only been two weeks! You will be relying on the English/Spanish translation much of the time right now, believe me. Secondly, Duolingo often introduces new concepts without explaining ‘why’. There is a ‘Tips’ section on every rung of the tree (in case you haven’t seen it) which is helpful to review- definitely do that- but it doesn’t cover everything.
The thing is, there is no context around what you are learning in Duolingo. So you have Basics 1, Basics 2, Phrases, (ok and Food 1, Animals, and so on) but a lot of it is random (‘The bee is in the sugar’, anyone?).
You may find you need to ‘fill in the gaps’, so to speak. You can go on YouTube and watch a couple of vocab or grammar videos. If you don’t understand why a word ends a certain way in one context but not another, or if you need to break down a phrase, etc, - google it. There are so many articles that explain these types of things in great detail.
You may find audio resources helpful too. I like ‘Learn Italian with Paul Noble’ - he does Spanish too. If you have a music streaming account/similar, see if there are any ‘Learn Spanish’ type content available. There are also other apps available- Memrise is free.
You’ll also likely find it easier to recall things you’re really interested in (for me it was food, haha!). So say if your hobby is baking, I’d look up baking related vocab in Spanish and learn that. It’s also a real confidence boost and every little you learn will get that ball rolling and attune you to learning even more in your target language.
Remember that it takes time and repetition to get somewhere with learning a language. And deliberate practise. If you’re not getting something you’ll need to work out what it is in particular you’re struggling with and actively go out of your way to understand, as with Duolingo it’s easy to become quite passive and just get by with guesswork if you don’t stay switched on.
Also it’s normal to be able to understand more (i.e. if it’s written down) than you can say/recall yourself. So right now you might not be able to say ‘The apple is on the table’ but if you read that sentence in Spanish, you may well be able to translate it.
I really started to improve when I set aside 10 minutes in the morning, 10 minutes on my lunchbreak and then 10 minutes or so right before bed. 15-30 minutes a day is great, just keep going with it. Consistency is key. Then I complimented Duolingo learning with looking up vocab, concepts, grammar, listening to Italian songs (and googling individual words that sounded interesting to me), watching ‘learn Italian for kids’ videos on YouTube and so on.
Other things I’ve tried include watching movies of interest in the target language (with English subtitles of course!). Even better if you can watch something you’ve seen a billion times in English (in my case, Harry Potter). You could also try sticking pictures with Spanish words around the Kitchen, etc.
Recommend you go on YouTube for Ted Talks on ‘How To Learn A Language’ too.
Hope there are enough tips there to fire you up 
You can do this! 