@Hope_gee your doctor sounds very inexperienced when it comes to birth control, I’d advice to talk to a different doctor in the future. There is no harm in being on birth control long term. 6 months isn’t even enough time to see how your body reacts, as it takes longer for it to fully adjust being off. The advice is that if you get off birth control it should be for a minimum of 12 full months. Going off and back on in a short amount of time actually increases your risk of developing blood clots. You’re probably going to be fine but keep an eye on yourself.
What you’re experiencing now is normal as you need to start as if you’ve never taken it again. It can also cause a pill that used to work fine now be causing issues, so if it’s still giving you problems a few months in you may need to try different types of pills or birth control to find something that matches you.