After long time without, three review invitations in two weeks. Coincidence, or do editors share lists of helpful reviewer names?
The journal editor (in chief) may not, but boards of editors have overlap and word does often spread that "X@Y is prompt, conscientious and fair."  

Or it could be random entropy. 

I wouldn't give it much thought. At best, you are being thought of as a good reviewer. At worst, it's a random quirk.  Choose the interpretation that makes you happiest.

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p.s. If you're feeling overwhelmed, it's entirely ok to tell a journal that you have to decline. Respond as soon as you can so that they can move on. Quick declinations (and referrals to potential other reviewers when possible) are also signs of good, conscientious colleagues. And I'm a strong believer that the good karma from these unrenumerated acts of conscientiousness will help in the long run.