All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
First of all, we ask Allaah to cure you from these whispers. You should know that if the matter is only whispers, then they do not harm the person but he should repel them and seek the refuge of Allaah from the devil.
Firstly, it appears that you are on much good but the devil wants to plot against you in order to spoil your religion and make your life miserable. Therefore, you should close all doors of the devil, and not let him control your heart in a manner that he would turn these whispers into belief.
For more benefit on the whispers of the devil and how to repel them, please refer to Fataawa 18353, 87525 and 88297.
Also, for more benefit on the virtues of the mothers of the believers and particularly of ‘Aa’ishah please refer to Fataawa when she married">82962, 83544 and 84846.
Secondly, it is not clear from your question what you mean by having bad feelings that raise doubt about the Prophet . In any case, you should know that you are obliged to believe in the Prophet love him, obey him and so forth. If you know the rights of the Prophet upon you and your heart becomes certain about them, then the whispers of the devil would not harm you.
Thirdly, concerning the fact that the Imaam (leader) that should be followed is the Prophet then this is something upon which there is no doubt. The absolute obedience is to Allaah and His Prophet while obedience to other than Allaah and His Prophet is restricted to and conditioned upon conforming to the Book of Allaah and the guidance of the Prophet . It should be noted that the Companions were keen on abiding by the guidance of the Prophet in all matters, both great and small. However, if there is an incident and they did not find a text of the Sunnah of the Prophet about it, then they would make Ijtihaad (a juristic opinion on matters which are not specified in the Quran or the Sunnah) about it. Indeed, their Ijtihaad is better for us than the Ijtihaad of others as they witnessed the revelation of the Quran and accompanied the Prophet and they knew from him and his circumstances what other people did not know. Also, it is confirmed that the Prophet said: "Hold fast to my Sunnah and the Sunnah of the rightly guided caliphs after me.” [At-Tirmithi]
Fourthly, the hair that grows on the neck is not from the beard, so it is permissible to shave it, because the definition of the beard according to the jurists is the hair that grows on the cheek and chin. The scholars stated that the hair of the neck is not from the beard; Imaam An-Nawawi stated this in Al-Majmoo’ quoting Imaam Ahmad .
For more benefit on the hair of the neck, please refer to Fatwa 87568.
Fifthly, serving the religion, making Da’wah (calling people to Allaah), establishing the Tawheed (Oneness of Allaah) and fighting against Shirk (polytheism) are among the greatest acts of worship; these are among the most rewardable acts of obedience by which a person gets closer to Allaah as by these acts one does not only benefit himself but he benefits others. So, you should be concerned about this and you should help those who strive in this path. Allaah Says (what means): {Help you one another in virtue, righteousness and piety.}[Quran 5:2]
Therefore, these are the matters that a person should be concerned with, as regards establishing the Hadd (i.e. the corporal punishment determined by the Islamic Law) on the apostates, then you have nothing to do with it [as this is a matter that is to be determined and implemented by the Muslim ruler].
Allaah Knows best.