I have struggled with this as well. I specialize in small to midsize businesses, but have done some larger commercial underwriting here and there. Trouble is that small businesses really are pretty different from larger businesses. Larger businesses have more exotic debt and equity, and that stuff really is just pretty freaking confusing if you're not used to dealing with it. My advice would be to try to find a job outside of your bank. Try applying for an analyst position in the equipment finance industry. There you're only focused on underwriting what's essentially a term note secured by the asset under consideration, so you won't have to get bogged down as much in valuations of receivables and inventory for lines of credit, etc. Aside from equipment finance, the only other thing I can recommend is getting a job as an entry level spreader at either your bank or another. There you'll spread financials until your eyes bleed, but, after a year or so of this, and dealing with more complex companies, you will find yourself more confident in it.
I'm kind of having the opposite problem from you though. For whatever reason, the job market here for commercial analyst just blows, and I'd like to break into consumer (I've done small businesses and read personal tax returns and personal credit reports for years), but I can't seem to get anybody interested in me for that kind of role. Hang in there, and good luck with it!