Oo, totally normal yan especially first time mo! A few of us sa barkada namin had irregular bleeding for the first 1-2 months after starting the injection, some had prolonged periods like yours, iba naman spotting lang for weeks. It usually settles down after 2-3 cycles kaya don't worry too much, but if it continues beyond next month or you're getting worried, best to check with your OB para sure lang, lalo na kung may cramping or unusual symptoms ka na.