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 is His slave and Messenger.
No one can know whether Allaah has accepted his acts or not since it is an unseen matter above the limits of human beings. However, a Muslim is obliged to worship Allaah while fulfilling all the necessary conditions and etiquettes of worship, and he should fear any deficiency in its performance; after that he only hopes to attain its reward from Allaah.
There are some signs that might be indications of the acceptance of good deeds, such as being inclined to do more good deeds, remaining steadfast after performing them [good deeds], etc.
The ways of strengthening one's faith include: exerting hard efforts in performing good deeds, being in the company of pious people, keeping away from bad places and supplicating Allaah to revive faith in our hearts. Ibn 'Umar narrated taht the Prophet said: "Faith becomes worn out in one's heart as clothes become worn out; so implore Allaah to revive faith in your hearts." [Al-Haakim and Al-Albaani]
Allaah knows best.