My daughter who is 19 has had similar issues. We just made our second trip to the ER. First time she was at 5.8. She experienced other adverse affects after the second dose of Moderna at the end of February but the low Hemaglobin became noticeable in June. Yesterday was the second time. The hemotologist is give her iron infusions starting next week. She wants her to have upper and lower GI scoped. We believe it's the vaccine. She was healthy before this.