The tired and achy is definitely normal, especially being on your feet that long at 28 weeks. As far as movement, my midwives have me doing daily kick counts starting at 28 weeks (which I have just reached). Their instructions were to pick a time when the baby is usually active, lay down and count how long it takes you to feel 10 movements. They said you should be able to feel 10 within 1 hour. If the baby is not moving after a few minutes, you can drink some juice and try again (I think it takes about 20 minutes for the baby to react to food). They sleep fairly regularly for 20-45 minutes, so I usually start counting when mine starts moving. If your baby has slacked off on movement really noticeably and you can't get him to react, I would call the doc.
Me College Literature Professor (36) and DH (35) married 7/05, together since 1/99; Mom to two lovely and fierce little girls: DD1 2/06 and, after 18 months TTC (and a couple years NTNP), DD2 born 7/3/12! Dedicated AP parent who is for selective (most) vaccination.