The rule is: when interests rate goes up, bond yield comes down
The rule is easy to understand: if everyone can buy a 4% bond on open market when interest rate goes up in 2017, why would anyone pay high price for a 3% bond issued in 2015?
Interest rate is effectively 0 now. It has nowhere go but up. So today's bond will worth less tomorrow when interest rate goes up.
For this reason, no bond buying for the near future.