Yes, us guys do get like that. It sort of reflects life. Sadly not upbeat and exciting all the time. Don't know if/how I'd cope if it was...
There is a myriad of reasons why we do anything - let alone learn or play music.
You need to determine those reasons, from your own standpoint.
Are you learning something to keep the teacher/parents/partner happy?
Are you learning something for your own gratification? Sounds like it's not working!!
Are you learning something because 'it needs to be learned - it's the stage I'm at'?
Are you learning something to be able to play it in an ensemble/exam?
These are only a few of the reasons for doing something, and it looks like if any of them apply, the end product doesn't justify the means for you right now. You need to come up with justifications that are valid for you. Goals need setting - realistic goals. Sometimes we just have to learn to play something but without a valid purpose, we'll be in your boat.
Visualise where you'll be in 6 months, 2 years time, etc. Think 'if I can play this piece which is boring the pants off me, how will it be of use?' Ask your teacher (you should have one!) for an answer to this - and if it's a convincing one, be convinced. They usually know better...
Another facet may be that you're not in the right frame of mind to practise when you try to. Tired after a hard day, worried about something, distracted, etc. etc. Work out a best time/place to play. There have been several questions posed on this site which address your sort of problem - hopefully someone can earmark them and more importantly, their answers.