Regular Expression for language – Computer Science Stack Exchange

I have a grammer with the following productions,

S -> aA | bC | b
A -> aS | bB
B -> aC | bA | a
C -> aB | bS

I have to construct regular expression for it. I derived words for this language and which are

b, aab, aba, baa, bbb, aaaab, aaaba, aabbb, abaaa, baaaa, …

So after I deriving the words I concluded that it’s a language of strings having odd number of b and having odd length.

Can you please help me to construct regular expression for it.

I appreciate your help.