Im not an expert and everyone is different, but I wouldnt think it is quite the start yet. The last few weeks are hard on you because of all the extra weight youre carrying, espesially if youre still working. If youre feeling shakey and sick, you really should give your midwife a call. Im sure everything is perfectly fine but they normally like to know about any little things like that. As for feeling more tired, that is definately normal at this stage.
Although not all ladies get these, here a few more signs you could look out for. Having a show or losing your plug. You will have a mucus discharge, possibly blood streaked. Do not be alarmed if it is blood streaked as this is normal. You may have these for a week or two before baby arrives. If your BH start to feel more like period pains and occur regulary, start timing them. Once they are regular for longer than an hour and dont ease after having a warm bath, call your midwife to ask her opinion on whether its the start of labour.
Again, you may not get them, but backache and mild period type pains are a more definate sign. Keep in mind though that these can stop and start several times before things really kick off.