I'm 5'8 130lb... so I should be pretty similar to you in size... small shirts usually fit fine for me... try finding the ones with smaller cuts for H&M/Walmart/Hollister, etc. Actually, those tight compression shirts from Walmart are actually too small with S, I have to wear medium there.

And for bike shorts, PBK usually carries those smaller sizes... 22-24 24-26 26-28... ?

I'm too cheap for jerseys so I wouldn't know where to find those.