I reverted back to Islam a few months ago, but I have waswas especially right before I start fasting. This makes it difficult for me to brush my teeth and have suhoor and everything in peace. I ask Allah to help me with this issue, is it a test from Allah? Is it a punishment, from shaitan, or just ocd? Please help
This is definitely shaytaan messing with your mind, you must fight and ignore them.
And those who strive for Us - We will surely guide them to Our ways. And indeed, Allah is with the doers of good. [29:69]
Keep on seeking refuge in Allah (أعوذ بالله مِنَ الشَّيْطَانِ الرَّجِيمِ) each time these thoughts come up and remind yourself that the evil could never hurt or control you, unless you allow them to.
...Indeed, the plot of Satan has ever been weak. [4:76]
And if there comes to you from Satan an evil suggestion, then seek refuge in Allah. Indeed, He is the Hearing, the Knowing. [41:36]
There is a principle in jurisprudence called اليقين لا يزول بالشك meaning: certainty cannot be dispelled by doubt
For example, It is permissible for a fasting person to use miswaak and toothpaste whilst fasting, so long as he is careful not to swallow anything. In fact using the miswaak is Sunnah when fasting and otherwise.
Therefore, ignore such thoughts until you are certain something has gone down your throat
Lastly, I advice you to Keep your tongue moist with the remembrance of Allah
Perhaps the book Hisnul Muslim will help you achieve that
I have used Saheeh international in this post