Which lube to use for conceiving?

Haapily married for 4 years, now we are planning child. We have being using vaseline as a lube,as all other lubes contains spermicide. I did'nt conceived, after trying for 3 months. Today i read that vaseline also kills sperms. I have read about using baby oil or olive oil also, but now kind of not sure.So Doc, what lube we should use to conceive?