How can one make up for missed prayers and fasting days, and are prayers and fasting from past years accepted if the questioner does not remember whether semen was ejaculated after masturbation or not?

If you do not know whether semen (maniyy) was discharged from you or not, the default assumption is that it was not discharged. Therefore, nothing is incumbent upon you until you are certain of its discharge. The characteristics of semen have been explained by us in previous fatwas.

Regarding making up prayers and fasting, you can refer to fatwa no. 137719.

To get rid of obsessive whispers (waswas), we advise you to supplicate and humble yourself before Allah, and to distract yourself from these whispers. We also recommend that you consult a trustworthy psychiatrist.