I'm not sure whether I am a positive or not,. I would like to be amore positive thinker for my health. I'm not sure whether I am a positive or not. I would like to be more positive for my health.

ALSO POSSIBLE: I'm not sure whether I am a positive or not. I would like to be more positive -- that is healthier.

I'm not sure whether I am a positive or not, but I would like to be a positive thinker for my health. I'm not sure whether I am positive or not, but I would like to be a positive thinker for my health.

"Positive" as a noun means a good thing/advantage, so you wouldn't use it as a noun here Needs a conjunction after the comma

I'm not sure whether I am a positive thinker or not, but I would like to be a positive thinker for my health. I'm not sure whether I am a positive thinker or not, but I would like to be a positive thinker for my health.

I'm not sure whether I am a positive thinker or not, I would like to be a positive thinkerone for my own health. I'm not sure whether I am a positive thinker or not, I would like to be one for my own health.

I'’m not sure whether I am a positive thinker or not, but I would like to be a positive thinker for my health. I’m not sure whether I am a positive thinker or not, but I would like to be a positive thinker for my health.

SMOOTHER: Being negative will lead to goodis sometimes good, but I think it's veryit's often tireding. SMOOTHER: Being negative is sometimes good, but it's often tiring.

Being negative willcan lead to good sometimes, but I think it's very tireding. Being negative can lead to good sometimes, but I think it's very tiring.

"Will" has a more definitive connotation, "can" makes the option more of a possibility "Tired" describes a someone/something that is worn out, "tiring" is someone/something that makes another thing tired

Being negative will lead to good results sometimes, but I think it's very tireding. Being negative will lead to good results sometimes, but I think it's very tiring.

Being a negative willthinker might lead to good sometimes, but I think it's very tireding. Being a negative thinker might lead to good sometimes, but I think it's very tiring.

Being negative willcan lead to good things sometimes, but I think it'’s very tireding. Being negative can lead to good things sometimes, but I think it’s very tiring.

I think thatMoreover, dwelling on the past idoesn't good way at least. Moreover, dwelling on the past doesn't good.

ALSO POSSIBLE: Moreover, dwelling on the past is fruitless.

I think that dwelling on the past isn't a good waything, at least. I think that dwelling on the past isn't a good thing, at least.

Or "it isn't good to dwell on the past"

I think that dwelling on the past isn't a good waything to do at least. I think that dwelling on the past isn't a good thing to do at least.

I think that dwelling on the past isn't a good way at least. I think that dwelling on the past isn't a good way at least.

I think that dwelling on the past isn't’t a good way to live, at least. I think that dwelling on the past isn’t a good way to live, at least.