Irregular bleeding is a normal side effect of the pill. No need to discuss with a doctor unless it keeps on happening/doesn’t stop for weeks, you may want to discuss changing pills with your doctor in that case. Cramps are also a normal side effect of the pill, I would recommend reading your pill’s pamphlet so you are aware of the potential side effects and know what’s happening if you experience them.
If you’re using your pill correctly it’s working. If you don’t trust your pill, you’re best to use condoms, it’s not worth stressing about it.