losing weight?

I weighed my almost 4 month old about 2 weeks ago and she was 13 lbs. today when i did it she was 12.6. It was on the same scale both times. I'm a little worried she eats 3-4 oz every three hours. The last couple weeks she has been spitting up more but I thought it was a normal baby thing because she's doing more floor time and rolling around like crazy. We have our 4 month appt in about a week but has anyone else little one lost weight? She was 10.5 at her 2 month appt. I'm not sure what normal gain is but wouldn't worry except she's gone down. FTM and I start googling and questioning when things like this happen. Thanks for any input!