birth control
"I got implanon as a teenager. After insertion (which hurt like hell) i had constant light spotting for 6 months. When I tried to get it taken out, the doctor couldn't find it. I went in a second time to a different GP and again he couldn't get it out. In the end I put up with it for about 2 years, and had to go under general anesthetic and have an operation in hospital to remove it- it was deep in the muscle and curved around itself. I now have a nasty scar as a result of cutting into the arm several times to have it removed. 

Now many years later- I have been trying to concieve for over 10 months without success. Whether or not this is related I don't know- but I wish someone had been there to tell my 17 year old self to stay well away"