1. Lack of Rest

Sleep plays an important role in our immune system. In fact, a study published earlier this year in the Archives of Internal Medicine demonstrated that people who got less than seven hours of sleep per night were nearly three times more likely to catch a cold than were people who slept for eight hours or more. Once you do have a cold, it will also take longer for it to clear up if you don't get adequate rest.

2. Low on Fluids

Fluids play an important part in your healing process. If your cold won't go away, consider drinking more water, Gatorade, or juice.

Being low on fluids can cause discomfort and dehydration, particularly because your water demands increase when you're sick, given the loss of fluids from drainage. In some cases, a lack of fluids in your system might contribute to prolonging your symptoms.

By drinking extra water when you're sick, you'll help to flush congestion out of your system. Increasing the amount of fluid in your system actually allows the mucus trapped in your nose and chest to flow better.

3. Taking Too Much Drying Medicine

Ever tried to sleep with a stuffed nose? But taking too much medication can actually make things worse and prolong your cold symptoms.

By overdoing it with drying medications like decongestants, you remove the moisture from your system, making it more difficult for the body to drain what's there. In addition, you may also be creating a host of other symptoms you didn't have in the first place. Using a decongestant nasal spray for more than three or four days, for example, can cause a medication tolerance to build up. And, taking too much of an oral decongestant can cause tremors, elevated blood pressure, and constipation.

4. Treating the Wrong Illness

The common cold can easily lead to and be confused with other ailments, such as sinus infections or allergies. Often, people convinced they've been suffering with a cold for a few weeks may not realize that they aren't getting better because they've been treating the wrong illness.

It's very common to confuse allergies with a cold because allergies typically have symptoms that are the same as or at least very similar to a cold. However, there are a few ways to tell the difference between the two:

Cold symptoms are usually from the neck up, and they usually peak after a few days.

Allergies, on the other hand, can present as a low-grade, persistent set of symptoms. Although allergies and colds can both cause a cough, runny nose and sneezing, they don't cause muscle aches, fatigue, and decreased appetite, which would all be more symptomatic of a cold than allergies.

One possible reason why your cold symptoms may be lingering is that you have a sinus infection. Very common development if you have had a cold for some time. Sinus infections can be difficult to diagnose, particularly in the early stages of infection. There are some telling signs, however, if you know what to look for. With a sinus infection, you're more likely to experience facial pain, a headache, fever, and green or yellow nasal discharge as opposed to clear.

5. Relying on Herbal Remedies

I'm sure everyone has heard the claims about some of the more popular herbal remedies out on the market for colds: Drink this and you'll never get sick again. Take that and your cold symptoms will be shortened by three days. Remember if it sounds too good to be true... it usually is! It's important to remember that just because the bottle says "herbal" doesn't mean it can't harm you. 

Echinacea has been touted as helping a cold, but two studies funded by the National Institutes of Health didn't find a benefit of using Echinacea for colds. Other research findings have been mixed.

In addition, counting too heavily on supplements like vitamins C and D to speed you through your cold is likely to leave you disappointed. Even though there is a great interest in vitamin C for colds, it has never really been documented that it works. There are no good studies to show its effectiveness, and it's been looked at pretty carefully over the last 20 or 30 years.

Today, the focus is more heavily on vitamin D and its potential to shield us from illness. Although there is a study on vitamin D that found that having low levels increased rates of the common cold, they haven't determined if taking extra vitamin D can shorten the duration or prevent the cold.

6. Exercising Too Hard