I had to take SlowFe post-partum due to low iron levels. I didn't exactly feel a 'low' in my energy levels; I just attributed it to uh well, you know, having a newborn and not getting more than 3 hours of sleep at a time!
The SlowFe wasn't bad. It is released slower so that you don't get all the constipation that you might with the regular iron supplements. That being said, I did hate that side effect because I absolutely never have a problem with constipation and something in the SlowFe prevents constipation, so I wound up with (TMI...gross...sorry) nasty soft poo that returned to normal once I was off the SlowFe.
And FYI just so you know...the iron will help your red blood cells pick up oxygen better. This is a very over-simplified way to explain it but think of your red blood cell and the oxygen that binds to it as the two parts of Velcro. With low iron, the 'velcro' is not as strong and the oxygen doesn't 'latch' on and your individual cells do not get enough oxygen needed for cellular activity, respiration, etc. You need oxygen to burn fuel in your body for energy. The deficit is what makes you feel sluggish and tired.
You can also eat red meat but the downside to that is many cuts of red meat are also high in saturated fat.