Just give him a little time. Many children are difficult to understand at his age. Perhaps your other child can help. Until my youngest granddaughter was about 3, I had to use her older sister as a translator. Her speech is now clear and precise.
Be willing to take some of the responsibility on yourself (even if it isn’t really your fault). Say something like, “I have trouble understanding you sometimes, so you have to be patient with me.” Or request, “Help me by pointing and I’ll know what you mean.” Whatever you do, resist the temptation to demand, “Slow down and speak more distinctly.” Such commands just make the child more anxious about his speech and may lead to a real problem.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.