Metamucil is water soluble fiber and is safe to be taken twice daily for as long as you want. It is fiber and your GI sytem needs this to function effectively. You will find that a lot of people on these boards have been taking Metamucil for years with no ill effects and only positive ones.
I think if things are sold in Pharmacies they have to put warnings on packets for official purposes. This does not mean that it is not safe to take for an extended period.
If you get bloating, yes this is normal until your bowels become used to the extra fiber. You also need to make sure that you drink at leat 6 to 8 glass of water with it to help wash it through your system. You also need to use it for longer than a week for it to become really effective. After a week, your body will only then becoming used to it.
If you have gas, then try some Acidophilus caps to rebalance your gut bacteria. Once rebalanced, gas should not be a problem. Keep them in the fridge and take them on an empty stomach. You can also eat live yogurt instead if you wish.