GREP Operation to Remove Return within Item Paragraph while Maintaining Return Between Items

Hello,

I have a document that is structured in the following way:

A0. Item A0 text.... ending with a period.

A1. Item A1 text.... ending with a period.

B1. etc.

...

In parts of this document, the item's paragraph has a return within it such that the following occurs:

C933. Item C933 text... \r

text continues as new paragraph (break may occur between words, numbers, following puncuation, etc.).

C934. Item C934 text...   .

C935. etc.

I am trying to figure out a GREP script that will remove any return within an item's paragraph. The GREP script would ensure that if a period followed by a return, followed by any sequence of 1 letter and 1 or more numbers followed by a period as seen here:

C934. Item C934 text...   .\r

C935. etc.

would be maintained; however, if the following occurs

C933. Item C933 text... \r

continues as new paragraph.

C934. Item C934 text...   .

the script would remove the return such that the above would appear as follows:

C933. Item C933 text continues in same paragraph.

C934. Item C934 text...   .

Thank you very much for any help you may be able to provide.