Had mirena (levonorgestrel) coil for 1 1/2 years and do not use condoms with my partner. Took antibiotics then had period more like spotting. Can I be pregnant?

Not likely. Iud's are one of the most effective forms of birth control. Irregular or absent periods are an expected side effect. Failure rates are 1%. Anytime you suspect pregnancy take a home pregnancy test. They are cheap, reliable and available at any pharmacy. If your test is positive you should see your doctor urgently because of the risk of tubal pregnancy (ectopic pregnancy).