If it continues, I'd speak to your midwife or Ob. I had continued pain which slowly got worse the first week after DS2 was born. By about day 10 I could hardly walk. I too noticed it more when I stood up.

When I went to see my ob he did an u/sound and found a very large clot still in my uterus. He prodded it a bit which thankfully dislodged it and broke it up and the pain eased after that.

If you aren't feeling better in a few days, I'd definitely get checked out.

Hope you're feeling better soon