Couple of things you can check:
1) check near where the water pipe enters your house - if you have a pressure reducing valve/regulator (usually right after the main shutoff valve in the house, but in warm country without freezing conditions may be in valve box with meter and outside shutoff valve), it may be set too low, if adjustable.
2) Your main shutoff valve may be corroding and blocking flow, assuming it is wide open.
3) You don't say if you have public water or a well - if on well, your pump pressure shutoff setting may be set too low, or if you have a sand filter tank it may be crudded up with debris due to lack of backflushing and be restricting flow.
4) Go to plumbing store and buy $5-10) a pressure gauge that can go on a hose bib (hose fitting) - and check your household pressure. Unless in the 40-70 pound range, sprinklers are pretty anemic. If really low, like 20-30 pounds when no water is running, then I would see if you can adjust your pressure regulator to a higher pressure. If not, you will need a plumber to correct that.
5) If your pressure in house and at faucet outside is 40 psi or better with no water flowing, then check it with water running full flow at a faucet. If it drops way off (more than 10-15 psi), then you could have corroded pipes (especially if galvanized or black iron, meaning likely 25+ years old), or could mean you have undersize piping. If the pipe coming into your house or anywhere in the line to the faucets outside is less than 3/4", then you are likely to have too much pressure loss in the lines for effective sprinkler operation.
6) If checking those things does nothing for your condition, then you are going to need a plumber - Search the List for well reviewed ones in your area.
7) One thing you can do it you have low pressure - not knowing what kind of sprinkler you have, but Gilmour Turbo Drive Oscillating sprinklers work well on low pressure - I can run two on long hoses and have someone running shower or washing machine and still get good coverage. These are the ones with the horizontal platic tube, NOT the arched metal spray bar type.
8) If you have more questions after checking things out, you can reply back using the Answer This Question button right below your question.