Feeling a little drained!

Well yesterdays long run was very hard work i got indegestion after 3 miles a stitch after 5 miles and hit what i can only pressume was "the wall" at 16 miles ish but i soldiered on and made it to 21 miles in a fairly presentable 3hr28 min average of 9.55
which i was quite proud of.
but the negatives that came from this i found quite scary it scared me that i have to go another 5 miles on top of this but some encouragement on the runnersworld forums has brought me back up and im feeling a little better about it now
i had maybe done too much over the week considering the half marathon pb last weekend but you live and learn less than 3 weeks to go so im a little nervy already but keep head down and keep plodding
On the diet front i feel quite positive still been avoiding the scale but feel like i may have had some success but it could just be all the effort yesterday thats depleted me a little
Keep at it
SNG