First of all - that's really weird if you actually did ovulate on the pill, because the pill stops that from happening. Did you take your pills correctly?
As for your IUD... The bleeding after sex sounds a bit annoying but at least it's gone. Bare in mind that cramps/period like pain is super normal and a very common side effect of hormonal birth control - you're likely to experience that on the pill, with the iud and with the implant. Unfortunately there's no sure way of avoiding it other than taking painkillers and using a hot water bottle to relieve it. As for your strings, it's actually very normal for them to wrap around your cervix - when they do this, can you feel them at all? If so, it's really not a problem. If you can't feel them at all, it's still most likely fine, but is worth having a doctor or nurse check to make sure everything is still in place.
Like I said, these issues are really typical of the IUD. A lot of women find that side effects die down more after a year. Honestly though, you may well find the same pain/cramps issue with the implant, plus new annoying side effects too. If you're seriously considering it, discuss it with your doctor. I personally think it may be worth waiting a bit longer to see if things settle more.