Can I follow both hinduism and sikhism?

Respected Sister,
Waheguru ji ka Khalsa, Waheguru ji ki Fateh!

In response to your question the undersigned wants to bring to your kind notice, as under:-

1. According to Hinduism:-

Three Gods rule the world.
Brahma: the creator;
Vishnu: the preserver; and
Shiva: the destroyer.

2. According to Sikhism:-

ੴ (Ik Onkar) (One Universal Creator God).

3. “Sikh” is a “Seeker of Truth” and “Sikhism” stands for:-

(i) Oneness of Humanity;
(ii) No discrimination owing to gender, race, caste, creed, or color;
(iii) No empty rituals & worthless religious practices;
(iv) No life after death theories. Rather, it stands for spiritual salvation/emancipation, during the life time, on getting rid of vices.

4. Further, Sikhism:-

(i) teaches a Sikh to live his life in the present, as per Hukam of Akalpurakh and teachings of ever living Guru, Sri Guru Granth Sahib;
(ii) expects a Sikh to earn an honest living, remain connected with Akalpurakh all the time and share his honest earning with poor and needy;
(iii) expects a Sikh to be compassionate, kind, tolerant and is to love all i e. he is to reach the mental state of seeing Akalpurakh in everyone and hence having friends only and no enemies;
(iv) expects a Sikh to serve the humanity, without any distinction of caste, creed and religion.

5. Guru Granth Sahib teaches a person/Sikh to get rid of vices, become a righteous/virtuous person. The goal of becoming a righteous/virtuous person was laid down by the First Guru Person Guru Nanak Sahib, in the first Pauri of Jap Baani itself, when he said:-

Kiv Sachiara hoiey, Kiv Kude Tute Pal,
Hukam Rajai Chalna, Nanak likhya Naal.

ਕਿਵ ਸਚਿਆਰਾ ਹੋਈਐ ਕਿਵ ਕੂੜੈ ਤੁਟੈ ਪਾਲਿ ॥ ਹੁਕਮਿ ਰਜਾਈ ਚਲਣਾ ਨਾਨਕ ਲਿਖਿਆ ਨਾਲਿ ॥੧॥

6. Once a person/Sikh achieves the goal of becoming a righteous/ virtuous person and becomes one with Akalpurakh and Shabad Guru, who are spiritually embodiment of each other, he will live a disciplined life and achieve the stage of spiritual equipoise and spiritual bliss. The main goal is to achieve spiritual emancipation/ salvation in this life itself since there is no concept of salvation/ emancipation, after death in Sikhism.

7. Imbibing the above teachings, of Guru Granth Sahib, is what is called Sikhi.

8. The undersigned would suggest that instead of taking Pahul (In common parlance called Amrit) straightaway, please change your life first, as per teachings of Guru Granth Sahib, and thereafter take any further decision.

9. Hope it helps. If you have any further questions, please do ask. If you find any deficiencies, please point out the same, for improvement in future.

Regards,
Your Brother