Many tropical diseases have a long incubation period, and it is possible to develop symptoms weeks after returning home (this is why it is important to keep taking anti-malaria prophylaxis for the prescribed duration after you leave a malarial zone). If you do get ill after you return home, be certain to tell your doctor where you have been. Alert him/her to any diseases that you may have been exposed to. Several people die from malaria in the UK every year because victims do not seek medical help promptly or their doctors are not familiar with the symptoms, and so are slow to make a correct diagnosis. Milder forms of malaria may take up to a year to reveal themselves, but serious (falciparum) malaria will usually become apparent within four months.
If problems persist, get a check-up at one of the hospitals that specialise in tropical diseases. Note that to visit such a hospital in the UK, you need a letter of referral from your doctor.
For further advice or help in the UK, ask your local doctor to refer you to the Hospital for Tropical Diseases or in the US to the Centers for Disease Control.