Veronica - i went thru a really tired stage about 16 - 17weeks. When was the last time you had your iron checked. I know that before i was preg, i had an iron deficiency, so i make sure i take my pregnancy multivitamins etc. Maybe next time you see your gp/obs/midlwife - mention it to them, they may recommended some bloods.
I also did get, not so bad anymore, that heavy feeling. When it was my AF, i used to describe it as my insides about to fall out! But, everything is fine for me, and i dont get them so much anymore. I just put it down to muscles stretching etc. Am not sure about the sore thigh muscles thou.