Why do some mantras feel ineffective even when I chant them daily in my mind?

Mera naam Arjun hai aur 4th September 2000 din mein 12 bje Mumbai mein mera janam hua h. Pichhale 6 mahine se main har subah “Om Namah Shivaya” ya “Sai Ram” jaise mantras mann mein repeat karta hoon, lekin mujhe lagta hai wo zyada farak nahi la rahe, anxiety waale episodes ab bhi hote hain: raat ko neend nahi aati, dimaag mein tension thoughts ghoomte rehte hain. Kai baar lagta hai ki mantra bas ek ritual hai, lekin dil se woh feeling nahi aati. Kabhi-kabhi jab main stress mein hota hoon, mantra skip kar deta ho, aur phir guilt ya regret hota hai ki kyun nahi kiya. Main chahata ho ki wo mantras effective bane, ki jab mein unhe bolun ya manun, tab anxiety kam ho jaaye. Kya problem meri technique mein hai, ya mantra chune mein? Aur kaise improve karun?