Can I sue if I was pregnant and I slipped and fell at a grocery store?

Yes, you make a claim against the store. Contact them and report what happened. They will ask what type of shoes, was your baby bump so large that you could not see if front of you, how large was the grape, any problems walking or with balance before, etc. They may be willing to pick up the medical bills [or difference between the billing and what your insurance paid] and give you a few hundred dollars for inconvenience, but your case has a low value so do not expect much. If their offer is too low, you can sue in small claims court, but the judge will wonder why you fell on a single grape and did the store have adequate notice of the grape so they could have cleaned it up before you stepped on it. It is not that clear the store is legally at fault.

Your case raises a question of negligence on the part of the store. An investigation by an experienced personal injury attorney should provide you with preliminary answers.