Ay, that's actually quite common with injectables, especially sa first few months pa lang, a lot of us experienced irregular bleeding or spotting after getting the shot, kaya don't worry too much! But since you're having consistent period and cramping ngayon, better check in with your OB or family planning clinic just to make sure everything's okay and to confirm if yan ang expected side effect for your body, or kung may iba pang adjustment needed. They'll know best kung normal lang siya or kung kailangan ng follow-up, lalo na first time mo pa lang sa injection. Rooting for you!