Political parties and interest groups might have a lot of things in common, but they are two different entities. A political party consists of people who are ready to pursue the same set of ideologies and are ready to gain power through elections. During elections, different political parties will have their candidates, which they will rally round in order to ensure that they win the elections.
However, after the elections, the losers become the opposition parties. Generally, all political parties campaign majorly with things like health care, social welfare, taxes, equality of rights, etc. Interest groups, on the other hand, are groups of people with common ideas about some issues.
They do all kinds of things within the ambit of the law to influence public opinion about certain things or issues. They differ greatly from political parties because they are newer platforms for people to contest in an election. Examples of interest groups are social groups, businesses, student unions, etc.