Still really confused about when Callie decides to ask you out
I've been working for her and porking her for days now to no avail
Callie's opinion of the MC depends on both working for her and asking her for fashion shows. Getting boyfriend status with her requires doing enough of both. If doing more work shifts doesn't help, then you probably need to see more shows (make sure you've seen every possible outfit at least once, and done the naked shows until they become repetitive). Also, if she ever asks you to do an all day shift of work, say yes - I'm not sure if an all day shift is required or if it just gives a big boost to the work counter, but I don't remeber having success with Callie's relationship path without doing an all day shift.
Once you've fulfilled her requirements, when you talk to her, she'll invite you on a picnic, and on the picnic you're given the choice of becoming a couple or just staying friends with benefits.
Note, however, that if you've done any threesomes with her and Evelyn at all, then the couple path with her is blocked and you'll never get the picnic invite (you can either be on a couple path or on the throuple/threesome path with her, they're mutually exclusive).
Compared to getting the couple invite, the throuple invite requires even more work, more shows, and doing enough threesomes (I think at least three). Finally, after the first threesome, she has to have a chance to talk to you about it (at least once for me, getting the throuple invite did not happen until I went and talked to Callie, allowing her to finally deliver the "let's pretend it never happened" dialog about the first threesome).