Whatever the mechanism, make your readers' lives easier by going for 3a and 3b or 3 followed by a and b. I wouldn't mix 3a and an unqualified b; and in general, unordered lists have a lead-in or introduction.
3. Eating on game daya. I finally ate today at almost one in the afternoon
b. I usually don't eat on game day but I ate today for some reason.
[snippy comment: the unwanted blank line before the second-level list is a present from the RTF editor]