Yes, you can use both at the same time.
When you stop using the Nuva Ring, the timing of your cycle may change. You may or may not keep getting your period at the same time of the month.
That's not necessary. You just have to insert or remove Nuva Ring on the same day of the week. The time of day is not critical.
You leave it in for the 3 weeks. Your cycle will adjust over time.
The same thing happened to me. You're supposed to leave the ring in place for the full three weeks to ensure protection. Supposedly you can spot any time that you're on the ring and be fine. If you phone the Nuvaring hotline, they'll tell you to go see your doctor if it keeps up/happens again next month.
As long as you put the ring in at the same time 7 days after you took it out you do not need any additional protection.
as long as you would any other time
When you stop Nuva Ring, you'll get your usual withdrawal bleed in the first week after you remove it. After that, if you had regular 28 day cycles prior to using Nuva Ring, you'll probably get your next period in 4-6 weeks. You may have some irregular bleeding or spotting during that time.
There are no known drug interactions between Nuva Ring and spermicidal foam, gel, film, or suppository.
If you used it last month for three weeks, had the ring-free week, and now are inserting the second ring, it starts working immediately.
Coming from a person who uses the Nuva Ring, I can say from experience that this is normal. The Nuva Ring is specifically designed deliver a low dose of hormones all the time. When you take out the Ring, your body recognizes that is it not receiving those hormones and it has it's period. When you don't give your body the hormones, it has it's period.
If you used Nuva Ring correctly during the previous three weeks, and are in your ring-free week, you have the same level of protection that you had in the prior three weeks. If you accidentally had the ring out for three days in the middle of your three week "ring in" time, you should use a back up method for the next seven days, and consider using emergency contraception.
If you start mid-cycle, you should use a back up method of birth control, like condoms or abstinence from vaginal sex, until you've had it in for seven days, at which time you'll get full protection. Effectiveness -- if 1,000 couples use Nuva Ring perfectly for a year, three will get pregnant. Since there are no perfect couples, pregnancy rates with typical use are higher than that, but there are no good data to date on typical failure rates with Nuva Ring. It's probably lower than typical failure rates with the pill, for which 8 pregnancies can occur among 100 couples using the pill for a year (higher for teens).