Advice??

Im 7 weeks today.. I haven't told my mom yet and although i have to i just dont want to. Yesterday was my sisters birthday and my family made her a whole breakfast and gave her 100 plus a new necklace. For my birthday i got 20 bucks. I was adopted and my sister is their real daughter. I just feel less than, i dont know if they know or care how it makes me feel.. Im happy for my sister but i cant help but wish i was treated like theirs.... Any advice