If you have to be at your destination by a particular time, be careful about waiting too close to your departure time before purchasing your ticket. If you do not have your seat reserved a week before you need to be there you run the risk of not being able to get a flight. This is especially true of flights to popular destinations and during peak travel season.
You're not crazy for thinking that a flight price has changed after searching it a few times in your web browser. Based on the cookies in your browser, flight prices do increase when a particular route is repeatedly searched, as the site wants to scare you into booking the flight quickly before prices get even higher. Always search for flights in incognito or private browsing mode to see the lowest prices.