Orange juice is not commonly a source of problems for the breastfed baby, but there's one way to find out for sure: Try eliminating the juice from your diet for a week or so. If you notice a change in your baby, try adding the orange juice back into your diet. If the problem comes back, you'll know to avoid orange juice in the future.
If OJ isn't the offender, here are some other things that could cause spit ups and/or fussiness:
Gastrointestinal illness: Only a doctor can diagnose this.
Sensitivity to something else in your diet: Have you been eating something new or taking a new medication, vitamin, or supplement?
Sensitivity to something in baby's diet: Have you fed her anything other than your milk?
Swallowed air: Fussiness and crying can cause baby to swallow more air, which can in turn cause spitting up.
Teething: When they're teething, babies drool more. Swallowing this extra saliva can cause spit ups.
A cold or allergies: These can cause baby to swallow mucus, which can lead to spit ups.
A growth spurt: Sometimes babies swallow more air during feedings during a growth spurt.
An oversupply of breast milk or fast let-down: Sometimes baby can take in more milk than she can handle — the extra comes back up.
Also keep in mind that the fussiness and spitting up could potentially be unrelated. Talk to the pediatrician if baby continues to be significantly fussier than usual or if she runs a fever or does not seem well. If baby simply continues spitting up now and then, but seems content, gains weight well, and has enough wet/dirty diapers, there probably isn't much to worry about (besides a few extra loads of laundry).