OPK advice please!

I don't have much experience with opk. Last cycle I never had a positive. Did US, letrozole, & a trigger injection with last cycle. No BFP :( I am now on cycle day 5 today. What day of your cycle did/do you start using opk? How often would you recommend, once or twice a day? I am feeling a little lost & discouraged. What should I do? Maybe it's just not even worth it to do the opk? I've also thought about starting to take my temp every morning to see if that helps. Any recommendation would be greatly appreciated.