The cause of a lot of my anxiety, and the reason I've been too frustrated to practice music for the last few months, is because I do not have an effective way to work on my relative pitch. I taught myself how to recognize intervals in isolation, both upwards and downwards quite well (and without needing reference songs). But I'm having a lot of trouble moving on to recognizing those intervals once there's more than one in sequence.
Playing melodies back on an instrument doesn't seem to be good practice (as it gives instant gratification and doesn't require you to actually think about the intervals), so I haven't been doing that. Instead I've been trying to work out the intervals in my head or on a piece of paper, then afterward going to confirm on my instrument. This works somewhat, but each time I have to manually go through each interval, listen carefully for it to match an interval I've memorized, and then move on to the next one from that. I don't think this is going to help me either, though. Does going through each interval, essentially "isolating" it from the melody, counter the whole point of trying to learn relative pitch?
So, I could try just guessing, and hope that each time I get a little bit closer to the mark, but this approach is also frustrating.
I need to have a way to practice my relative pitch before I can keep practicing music, it's just too upsetting knowing that I'm not getting any better at it. How can I practice recognizing intervals in sequence and improve my relative pitch?
Edit: I should mention that I have ADHD and have a very difficult time focusing on things like ear training when they don't seem to be helping me progress. If it's clear to me that progress is being made, I can keep my anxiety under control.