I'm a 32 yo male. i've been noticing recently that my erections are not keeping up with the sex drive. sex is no my mind all the time, but i struggle to match that with hard erections.  i get half ass erections, and struggle to even get it up quick enough. it hasn't always been the case. I used to have rock hard erections the minute i am stimulated. this is irritating me. what can i do? please help?