Hello,
The bowel habits of a child sometimes altered when you shift them from liquid diet to semi solid or solid diet, but it soon settle down with some adjustments in the food. One of the common reason behind the anal inflammation is hard stool, as hard stool cause rashes and the area becomes red and inflammed. Fruits like apple and banana may cause constipation so give your baby lesser of banana and apple until the hard stool problem has been solved, in cereals give less rice which may also cause hard stool as all these are stool binders. Avoid giving him excess of potatoes too.
The solution to your problem is give your baby more liquids as juices(orange and prune juice you are already giving is good and other juices can be given) , soups as vegetable soups(give green vegetables soup), daal soup(legume's soup) can be given. Sometime dehydration may also lead to constipation so more liquids will help in getting relief from dehydration too.
In cereals instead of rice you can give oatmeal or barley cereal.
in fruits instead of apple and banana give him peaches, apricorts,pears etc.

For anal inflammation apply petroleum jelly,zinc oxide and coconut oil alternatively on anal area as all these will make a protective layer on skin and has soothing effect on skin. Use each of these differently. Keep the area clean and dry. Change the diapers frequently. When more inflammation is there then use less diapers as friction with skin will also increase more inflammation.
If you have changed your formula milk brand then consult your doctor because formula milk might be behind one of the reasons for constipation sometimes.
Some people use stool softeners and glycerine suppostiries for constipation, if you are also using the same then dont use them for long otherwise your baby will get habitual to it.
Try these dietary habits regularly and apply all these regularly you will soon see positive results. In case of any emergency you can consult a nearby dermatologist. I hope you are satisfied with my answer.
Thank you.