Having major problems with doubts & waswas?

Salaam...Just recently my brothers friend came over with his new puppy to show my brother. They stayed outside but now im having doubts that if the puppy licked my brother on the hands for example, then whatever he touches will become impure. Im also scared that i might end up touching something that he touched which could end up in my Salah not being accepted. Ive heard that since Allah SWT doesnt want to overburden you, that u can use benefit of the doubt, which means i could just ume that the puppy didnt lick my brother. Its not so easy for me to do this though because of waswas. None of my other Muslim friends would think like this, its just me, and it gets sooo stressfull. What should i do? Do i just use benefit of the doubt since i didnt c what happened? This waswas has been happening alot to me lately, and im starting to get depressed over it. If anyone has any websites that could help, then please tell me what they are. If u have any information or tips that may b usefull to me then please tell me.