Is there a way to check the existence of a specific word from the string(Text)

 Is there a way to check the existence of a specific word from the string.For example if the text is

"My_name_is is Uday"

If the above one is a string , i would like to check only for "is" and not "is" present in the My_name_is.

For this i would like to use Instr

So when we are using Instr("My_name_is is Uday",'is',1,1) then the output is 9.

But what i am expecting is the position of "is".

so if the string is "My name stagis and there is great road ahead"

Then i am looking at is before great.