I got a Sirius Sportster 5 home kit for my birthday and I can't seem to get a signal that stays strong?

I set it up on the edge of my balcony about 4 or 5 hours earlier and I had full signal strength. I left to go get some groceries (45 minutes) and came back to no signal. Nothing moved and now I can't find a good signal no matter which way I face my antenna. Why would I have a 3 bar signal and then suddenly have no signal? Any help is appreciated, thanks!!