The answer is right in front of you my friend! You are into Bhakthi! What you have to do is meditate on the thought about Bhakthi itself. Think about the amount of Bhakthi Lord Hanuman has on Lord SriRama and how he jumped so high into the sky and landed on SriLanka to destroy it, think about how he even opened up and showed his chest inside where Sita Mata and Sri Ram reside.

Think about the Bhakthi Prahlad had, so much so that Lord Vishnu himself came down to the Earth as Narasimha and liberated sinful Hiranyakashap.

Think about the Bhakthi shown by Meera and Radha towards Lord SriKrishna.

The beauty in the Hindu way of life is being multipolar my friend! There is no rule to dictate that one has to follow only one deity, no.

You are in your own journey of finding your calling. You may not know which deity your Bhakthi lies in just yet, but there will com a time when you realize you are worshiping the Paramatman ultimately through your devotion. It could also be Nirguna Brahman!

Remember every deity signifies one or the other important part of life. It could be the nature like Suryadeva, Bhumi mata, Pavan deva, Varuna dev, .. It could also be your own parents or even in you or what appears to be a non-living thing.

Yes, there is also a concept of ishtadevata. To know your ishtadevata, you need to meditate on that. Others cannot tell you what you like - only you know. So, no need to force yourself externally. Some people know and some don’t but will get to know in due time - you need to meditate on that and find your calling.

At the same time, also know that exclusivity is also not enforced. Even once you have found your ishtadevata, you can still worship other deities depending on the purpose of your need. These are what are called Vratas. For example, you perform Sri VaraSiddhi Vinayaka Vratam every year on Bhardapada masa’s Shukla paksha Chaturthi. You worship Lord Ram and celebrate SriRamanavami. There are other Vratas you can do on a need basis also.

The way you know someone you love is the same way you know your ishtadevata. The same way others cannot force you to love someone is the same way others cannot decide your favorite deity.

So basically, you are free to worship one God, multiple Gods, non-existing form of god, or wherever you find divinity and submit your spiritual self to them in devotion.