pregnant on depo

I've been on depo for about 4 years. I have a question for you ladies, the longer you been on depo does it become less effective?!?! For past couple weeks I've been so exhausted and all I've wanted to do was sleep. No I've gotten to where I'm peeing a lot more than usual. I was up & down last night all night peeing. I went to bathroom this morning at 830 then went again at 9. & I didn't have much to drink yesterday AT ALL. & ive been cramping on & off since yesterday but they are very light cramps. I just need some advice. Thanks ladies