Regarding contact lenses.

I have been wearing contacts for years now ..

I have no idea why sometimes my vision is super clear while sometimes it is blurry?

I bought contacts which are 100 degree lower than my actual.

Why is that so?

Last few month , My contact lenses gave me like 20/20 clear vision depite 100degree lower but recently i changed and my vision is back to the normal vision. 

Anyone care to share any advise?

i think you should be asking this to an optometrist or the people at the glasses shops