To help your teeth rebuild from the inside, calcium is always a good start. A nice amount would be 1000 mg per day. There are a few different types of calcium, calcium citrate being the simplest to absorb. Be sure to take magnesium with the calcium citrate, for best absorption. There are several brands of calcium citrate which also contain magnesium, so you don't have to purchase them separately.
I have the same problem with my enamel and have seen great improvement since taking these vitamins. I take 500 mg of calcium (with magnesium) in the morning with breakfast and another 500 mg with dinner.
It's safe to continue eating citrus fruits, just make sure to rinse your mouth with water after. Always wait 30 minutes to brush after you've eaten anything acidic or sugary.
Another thing I did was to purchase a very soft-bristled child's toothbrush. I brush very gently, only applying extremely light pressure.
It took about 3 months of taking the calcium before I started seeing improvement with my enamel.
I hope this helps and I wish you a healthy, happy smile.