I feel exactly the same. A few weeks ago I had a blood test which came back my iron levels were really low (should be around 20 apparently I mine came back at 4). Doc said for me to get some iron tablets & B12 tablets which I took until he said too. I felt better but now I am not taking them (as he said to stop at 36wks) I am back to being very lethargic & tired again. I hate feeling like this! Makes me worry how I will cope with my 20mth old and a newborn when bub arrives.