"إن الله تجاوز لأمتي ما حدثت به أنفسها"
"God has condoned my nation(Muslims) for what they thought to themselves"
thinking about stuff in your brain isn't a sin, in fact, in some cases, it might be praised to do so. Remember this rule in your brain, without thinking whether a god exists or not, it isn't considered all that "belief".
Sometimes you might think about bad stuff that are actually bad(not useful, useful is like questioning yourself does god exist and thinking of reasons)
and in these cases, you ask God to make the devil go away and try not to think about it, but it isn't sinning.
It is a good thing you feel a bad feeling for thinking about your God, but thinking you shouldn't pray(or do anything for Allah) is the biggest sin and is how devil leads people to the pit of hell! God said:
"وَالَّذِينَ إِذَا فَعَلُوا فَاحِشَةً أَوْ ظَلَمُوا أَنفُسَهُمْ ذَكَرُوا اللَّهَ فَاسْتَغْفَرُوا لِذُنُوبِهِمْ"
"And the ones(mentioning good doers right before) who, when they commit any indecency and wrong against themselves, instantly remember Allah and implore forgiveness for their sins"
Whenever you feel you dont deserve to pray to him or "what is the point" know exactly that it is from the devil to get you astray!
Now to a very important misconception, not all devils get chained in Ramadan, in fact, only the "bosses" of the devils get chained or the ones that are of huge evil(like Satan himself) but normal demons don't, there are Muslim demons, and even non-Muslim demons, the ordinary ones don't get locked up, and even if they did, for every human being since he is borned there is a devil that is stuck to him everywhere he goes, the only time he leaves him is when the human himself dies(causing the devil to die as well) the only exception was Prophet Mohammad(PBUH), God helped him convince his devil and made him a muslim! so don't get that sad, there are devils even in Ramadan, after all, they are a race! Just like human beings are, God wouldn't just lock up a whole race each year for a whole month!
In conclusion, whenever you get bad thoughts try praying for God or reading some Quran and ask God to make the devil go away.