I'd say "darle muchas vueltas al asunto". you are overthinking it. ~~ le estas dando muchas vueltas al asunto. Or maybe you are thinking it in a deep way, "reflexionando" , "analizando". Maybe if you could give an example in english, I could help you a bit more.

Puedes usar "Dar cabeza" o "Dar mucha cabeza" (in english: to give head) Eso seria pensar algo o pensarlo mucho.

*How(I am in such a hurry)

How* do you say...? You should put it in a context, in a sentence, as, depending on the context, the translation may change.