My book is a mess, help!

So...I've been fumbling around with the same characters for about three years now, and I've wound up with a handful of short stories, one novella, and a near-complete (but short!) first draft of a novel involving them. Originally, the short stories and novella were in a collection with other unrelated stories, a book I'm really proud of, but the novel has felt lacking for a while, and I got the idea to merge all the material into one book and expand things--something that my mentor has really pushed for, an idea I've resisted until now because I love the flow of the short story collection. However, I've had a two-month dry spell thanks to a very overwhelming full-time teaching gig, and I started rethinking both books in part just because I need a way back in. I think, with some work, the merged stories could make for a really fun and cohesive book, but I'm completely overwhelmed by the amount of material I have, adjusting the timelines to make things fit together, adding new material, etc. I think part of the problem is that I don't have complete faith that this is the best route to take, and part of the problem is that I see myself as a writer of short fiction who suddenly has a chaotic 75,000 word manuscript, which feels like way too much to handle. I have confidence that it could work as a longer book with multiple points-of-view, but I'm stuck with where to begin, it's just so huge to me.

Also: an agent whose representation I'm seeking loved the short story collection and asked me to write a novel to pair with it, which is how the original novel emerged. I asked her how she'd feel about me dismantling the story collection to expand the novel, but I haven't heard back yet. Though I don't want to be swayed by industry expectations, I want to ask, what do you think is more marketable? A short story collection and a short novel (perhaps 55k) or one novel in the 80-90k range? All literary fiction. What should I do? I almost finished the novel but hit a dead end with it, and adding in the other POV character invigorated me a little bit...but I still can't really write forward, and I think it's because I'm overwhelmed and lack confidence. I don't know how to get back on track. Would really appreciate advice!

Thank you guys for these responses. The novel-in-progress, before I merged it with the other stuff, was about 50k and almost done, so maybe I should just keep it separate and think about how to expand it? I'm really stuck with everything and have been for a while--not sure how to finish it, not sure where else I could expand. The agent wants the novel to be at least 60k, but I'm just not very comfortable writing long stories. Novella-length is my favorite.

I don't think it's a bad novel--I'm just stuck with it and I can't for the life of me figure out how to make it longer. I'm also stuck with the ending, but my gut sense is that it doesn't need more than 5,000 words to reach its conclusion because most of the plot points have been resolved. It was on pace to be novella-length until the agent told me that she needed at least 60k, so even reaching 50k was huge, but writing long works just doesn't come naturally to me. I'm endlessly frustrated by these industry expectations! I wonder if I should add other POV characters? It's the only thing I can think to do to expand it.

Yeah, that could work! I just have to brainstorm possibilities and keep an open mind. Thank you all for these responses, they were helpful and comforting

Okay, I think I may have solved my problem...I have two stories about the protagonist, situated before the main events of the novel, and I think they work well as a kind of prologue. They were, at one point, included in this book, and weaving them back in brings the unfinished draft to 56,000 words. I'll have to write a few new stories to replace them in the collection, but I figure the novel would be the book to get published first anyway (KNOCK ON WOOD). God, I hate this word count thing! I'm so grateful that the agent is willing to consider a 60K book since I know that it'd be impossible for me to make it to the standard 80K! And the nice thing about this is that I can leave my novella intact, which my gut was telling me to do.