Doubts regarding ghusal

Q: What if I do ghusal and then also attend salaah but later I have a doubt whether the ghusal I did was valid or not. The reason being that I think the water didn't wet all the hair on my body. Should I do the ghusal again and repeat the salaah which I attended?

Feeling jealous if husband takes a second wife

Q: Allah created both men and women differently such that a woman does not naturally feel to have more than one spouse at a time.

1. My question is that if it was in the nature of a male to have more than one wife as created by Allah then why are there naturally the feelings of jealousy or insecurities and intolerance that a woman feels about it? My mind and heart both know that Allahs plans are the best and I blindly trust in them but then why I feel annoyed and really bad about the fact of sharing my husband with someone else. I even feel annoyed when my husband teases me about angels of Jannat? Why has Allah put this feeling in us knowing the natural tendency of males? 

2. Though I know that there is nothing wrong in having more than one wife but I still feel uncomfortable and jealous about this fact. I would never be able to stand the fact of my husband marrying someone else. Does that mean that I am not a good believer as my husband constantly keeps saying that if I cannot tolerate the fact of my husband having another wife (suppose) then I am not a good muslimah. Is that so?

Authenticity of the dua for Rajab and Shabaan

Q: I would like to know whether reciting the following famous Dua is Sunnah/Permissible/Bidah:

اللَّهُمَّ بَارِكْ لَنَا فِي رَجَبٍ وَشَعْبَانَ، وَبَلِّغْنَا شَهْرَ رَمَضَانَ

Is there a strong command or a sign of permission from Rasulullah Sallallahu Alaihi Wa Sallam regarding the recitation of this Dua in the months of Rajab and Shabaan?