It could very well be that you're pushing your palatal vault up high?

If you were my brother, I would suggest to stop doing what you're doing.  Typically there would be some level of retraction... but it may not.   Might have to widen with braces or something so it can drop.

Well, you could start with the acknowledgement that correlation does not equal causation and that it's entirely possible that your tear troughs and dark circles would have worsened in the same time period even if you hadn't mewed. Dark circles can appear or worsen for a number for reasons, two examples being iron deficiency and weight loss. My tear troughs look more pronounced at lower body fat %'s. It's worth ruling out every possible cause for these things before linking them to the mewing. 

The other possibility is that your tear troughs and dark circles haven't worsened, and that since you started mewing your mind has become preoccupied with the monitoring of physical changes in your face. It's really easy to delude yourself into thinking a negative change has taken place when it hasn't. Especially when you're looking at photos which vary in lighting, angle, ambience etc. 

First off, congratulations on mewing for 5 months.  I second Alpha Minus, in that our perceptions are always changing and you might in fact look quite better than ever.  But if you are experiencing heightened discomfort, please do yourself a favor and visit a professional who can make sure that you're not in real trouble.

    But also, as your bones adjust there may be a buildup of tension in your face.  I suggest getting a professional cranio-sacral massage or at least treating yourself to a good head and face massage.  Take a good bath in epsom salts and after you've dried off, if you are able, lean over so that your head is hanging upside down and massage your whole head and face for ten minutes.  After a few nights of this try and tell me you don't look and feel better.  

    Take care!