They're both possible. Is tells us the state of your health: much improved. "Improved" is an adjective in this sentence.
Yes. Your health now is much better than it was last month.But it's talking about "last month". Why is "is" [STRIKE]is[/STRIKE] used? Or "Why does it use 'is'?" Is it because the word "over" is used?
It's a horoscope; it purports to prognosticate what your health is going to be like for the rest of this month.
(Or it did back in 2017 when it was printed. Why are you reading that ancient stuff?)
(See How the Stars Can Predict Your Future by Horace Cope)
Because I forgot I bought that book. Now I use it to learn English.
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