regex - Adding Carriage Returns without deleting numbers -

fellow forum members,

need little setting notepad++ regex following. have sentences preceded outline level numbers read single text string shown belov:

1. sentence bla bla 2. sentence bla bla 3. sentence bla bla 3a. sentence bla bla 3b. sentence bla bla 3c. sentence bla bla

my goal data it's shown below adding new line carriage returns in front of outline level numbers @ same time need regex not care outline level numbers (i.e. 1. 2. 3. 3a. 3b. 3c.). need regex leave these numbers alone , insert new line carriage returns in front of these numbers data looks shown below:

1. sentence bla bla

2. sentence bla bla

3. sentence bla bla

3a. sentence bla bla

3b. sentence bla bla

3c. sentence bla bla

i have been experimenting following wild card characters:
.+? also: \r\n

the problem can't work. appreciated. in advance.

search:

(\b\d+[a-z]?\. ) 

replace:

\r\n\1