Welcome, Cale.

It sounds like some things are working for you and some things aren't. Some other people have posted resources that would be good to read. It's sometimes hard to figure out whether what you feel on any day is because of a certain med, its dosage, withdrawal or readjustment from one you've been on previously, and sleep, food, coffee/alcohol, will all also change that from moment to moment. Journaling helps. Also, since you're aware that you're being irritable with your girlfriend, you definitely are competent to acknowledge that and communicate it to her and apologize if necessary. Don't be too hard on yourself for being interested in people outside your relationship. Life is complex and you're young and dealing with a lot of difficult things that many people don't have to tackle. Best to you.